<html><head><meta name="color-scheme" content="light dark"></head><body><pre style="word-wrap: break-word; white-space: pre-wrap;">\makeatletter
\@ifundefined{HCode}
{
\documentclass[CRBIOL,Unicode,screen,biblatex]{cedram}
\addbibresource{crbiol20240768.bib}
\newenvironment{noXML}{}{}
\newenvironment{Table}{\begin{table}}{\end{table}}
\def\thead{\noalign{\relax}\hline}
\def\endthead{\noalign{\relax}\hline}
\def\tabnote#1{\vskip4pt\parbox{.8\linewidth}{#1}}
\def\tsup#1{$^{{#1}}$}
\def\tsub#1{$_{{#1}}$}
\def\xsection#1{\unskip\noindent}
\RequirePackage{etoolbox}
\usepackage{upgreek}
\def\jobid{crbiol20240768}
%\graphicspath{{/tmp/\jobid_figs/web/}}
\graphicspath{{./figures/}}
\newcounter{runlevel}
\let\MakeYrStrItalic\relax
\def\refinput#1{}
\def\back#1{}
\def\0{\phantom{0}}
\def\ubreak{\break}
\DOI{10.5802/crbiol.178}
\datereceived{2024-09-20}
\daterevised{2025-05-28}
\dateaccepted{2025-06-02}
\ItHasTeXPublished
}
{\documentclass[crbiol]{article}
\usepackage[T1]{fontenc}
\def\CDRdoi{10.5802/crbiol.178}
\let\newline\break
\let\ubreak\relax
\makeatletter
\def\selectlanguage#1{} 
}
\makeatother

\usepackage{upgreek}

\begin{document}

\begin{noXML}

\CDRsetmeta{articletype}{review}

\title{Evolutionary convergences and divergences in sympatric species:
\textit{Morpho} butterflies as a case study}

\alttitle{Convergences et divergences \'{e}volutives chez les
esp\`{e}ces  sympatriques : le cas des papillons \textit{Morpho}}

\author{\firstname{Vincent} \lastname{Debat}\CDRorcid{0000-0003-0040-1181}}
\address{Center of Interdisciplinary Research in Biology (CIRB),
Coll\`{e}ge de France, INSERM, CNRS, Place Marcellin Berthelot, 75005
Paris, France}
\address{Institut de Syst\'{e}matique, Evolution, Biodiversit\'{e}
(ISYEB), Mus\'{e}um national d'Histoire naturelle, CNRS, Sorbonne
Universit\'{e}, EPHE, Universit\'{e} des Antilles CP 50, 57 rue Cuvier,
75005 Paris, France}

\author{\firstname{Manuela} \lastname{L\'opez-Villavicencio}\CDRorcid{0000-0001-6216-9547}}
\addressSameAs{1}{Center of Interdisciplinary Research in Biology
(CIRB), Coll\`{e}ge de France, INSERM, CNRS, Place Marcellin Berthelot,
75005 Paris, France}
\addressSameAs{2}{Institut de Syst\'{e}matique, Evolution,
Biodiversit\'{e} (ISYEB), Mus\'{e}um national d'Histoire naturelle,
CNRS, Sorbonne Universit\'{e}, EPHE, Universit\'{e} des Antilles CP 50,
57 rue Cuvier, 75005 Paris, France}

\author{\firstname{Violaine} \lastname{Llaurens}\CDRorcid{0000-0003-1962-7391}\IsCorresp}
\addressSameAs{1}{Center of Interdisciplinary Research in Biology
(CIRB), Coll\`{e}ge de France, INSERM, CNRS, Place Marcellin Berthelot,
75005 Paris, France}
\addressSameAs{2}{Institut de Syst\'{e}matique, Evolution,
Biodiversit\'{e} (ISYEB), Mus\'{e}um national d'Histoire naturelle,
CNRS, Sorbonne Universit\'{e}, EPHE, Universit\'{e} des Antilles CP 50,
57 rue Cuvier, 75005 Paris, France}
\email[V. Llaurens]{violaine.llaurens@college-de-france.fr}

\shortrunauthors

\keywords{\kwd{Evolution}
\kwd{Adaptation}
\kwd{Speciation}
\kwd{Sympatry}
\kwd{Butterflies}
\kwd{Flight}
\kwd{Sex chromosomes}}

\altkeywords{\kwd{\'{E}volution}
\kwd{Adaptation}
\kwd{Sp\'{e}ciation}
\kwd{Sympatrie}
\kwd{Papillons}
\kwd{Vol}
\kwd{Chromosomes sexuels}}

\thanks{European Union (ERC Consolidator grant OUTOFTHEBLUE, project
number 101088089)}

\begin{abstract}
How do closely related species interact in sympatry? And how do these
interactions influence the evolution of their traits and the dynamics
of species diversification? In this review, we show how recent research
on the evolution of \textit{Morpho} butterflies contributes to address
these questions. We first show how sympatric species have colonized
different vertical strata in the neotropical forest and how this
divergence has produced cascading adaptive effects on behavioural
(flight) but also morphological traits, including wing size, shape and
coloration. We then focus on the evolution of peculiar dorsal blue
coloration within the genus \textit{Morpho}. During flight, the blue
iridescence produces bright flashes that confuse predators and likely
enhance the escape abilities of these butterflies. In turn, predators
learn the association between such conspicuous coloration and escaping
capacities. Such learning favours the locally abundant colour pattern
and promotes the local convergence in sympatric species. However, this
tight resemblance also induces sexual interference between mimetic
species. Capture--Mark--Recapture data uncovered that mimetic species do
not fly at the same hours: competition seems to have driven the
divergence in the timing of flight activity between species. Overall,
sympatry therefore promotes the intricated evolution of convergent and
divergent traits among tightly related species, that jointly facilitate
their coexistence. Whether ecological speciation was involved in this
evolution is an intriguing open question. At the genomic level,
analyses revealed a faster evolution of the sexual chromosome Z as
compared to the autosomes, with extensive rearrangements and molecular
signals of positive selection: these data thus suggest an important
role for the Z chromosome in adaptive evolution in \textit{Morpho} and
possibly in speciation. Paving the way for future research, these
various, multilevel studies show that \textit{Morpho} are not just
those showy butterflies in the box: they can also teach us much about
evolutionary processes.
\vspace*{-2pt}
\end{abstract}

\begin{altabstract}
Comment les esp\`{e}ces \'{e}troitement apparent\'{e}es
interagissent-elles lorsqu'elles vivent en sympatrie ? Et comment ces
interactions influencent-elles l'\'{e}volution de leurs traits et la
dynamique de la diversification des esp\`{e}ces ? Dans cette revue,
nous montrons comment les recherches r\'{e}centes sur l'\'{e}volution
des papillons {\textit{Morpho}} contribuent \`{a} r\'{e}pondre \`{a}
ces questions. Nous montrons d'abord comment des esp\`{e}ces
sympatriques ont colonis\'{e} diff\'{e}rents \'{e}tages au sein de la
for\^{e}t n\'{e}otropicale et comment cette divergence en terme de
micro-habitat a influenc\'{e} l'\'{e}volution adaptative d'une
s\'{e}rie de traits comportementaux (vol) mais aussi morphologiques,
tels que la taille, la forme et la coloration des ailes. Nous nous
concentrons ensuite sur l'\'{e}volution de la coloration bleue
iridescente de la face dorsale des ailes observ\'{e}e chez de
nombreuses esp\`{e}ces du genre {\textit{Morpho}}. Cette iridescence
bleue des ailes produit des flashs lumineux durant le vol de ces
papillons et perturbe vraisemblablement la d\'{e}tection de leur
trajectoire par les pr\'{e}dateurs. Cette coloration, associ\'{e}e
\`{a} un vol erratique pourrait ainsi am\'{e}liorer les capacit\'{e}s
de fuite de ces papillons. A la suite de leurs \'{e}checs, les
pr\'{e}dateurs peuvent apprendre \`{a} associer cette coloration
voyante aux capacit\'{e}s de fuite des papillons qui les arborent. {Un
tel apprentissage peut favoriser des convergences \'{e}volutives vers
un m\^{e}me type de coloration iridescente, facilement identifiable par
les pr\'{e}dateurs, dans diff\'{e}rentes esp\`{e}ces vivant dans un
m\^{e}me environnement. Cependant, cette ressemblance \'{e}troite
induit \'{e}galement des interf\'{e}rences sexuelles entre les
individus de diff\'{e}rentes esp\`{e}ces mim\'{e}tiques partageant un
m\^{e}me habitat. Des exp\'{e}riences de capture-marquage-recapture en
milieu naturel ont ainsi r\'{e}v\'{e}l\'{e} que les esp\`{e}ces
mim\'{e}tiques ne volent pas aux m\^{e}mes heures : la comp\'{e}tition
entre les m\^{a}les pour l'acc\`{e}s aux femelles pourrait \^{e}tre
\`{a} l'origine de la divergence dans les horaires d'activit\'{e}
entre les esp\`{e}ces. La sympatrie favorise donc, chez des esp\`{e}ces
\'{e}troitement apparent\'{e}es, l'\'{e}volution de traits
convergents et divergents, qui facilitent conjointement leur
coexistence.} {La question de savoir si l'\'{e}volution de ces traits
a particip\'{e} au processus de sp\'{e}ciation ou est une
cons\'{e}quence du renforcement des barri\`{e}res aux flux de g\`{e}nes
entre esp\`{e}ces reste ouverte. Au niveau g\'{e}nomique, une
\'{e}volution plus rapide du chromosome sexuel Z par rapport aux
autosomes a \'{e}t\'{e} document\'{e}es, avec notamment des
r\'{e}arrangements plus pr\'{e}valent et des signaux mol\'{e}culaires
de s\'{e}lection positive plus marqu\'{e}s sur ce chromosome. Cela
sugg\`{e}rent que le chromosome Z pourrait jouer un r\^{o}le majeur
dans l'\'{e}volution adaptative chez les} {\textit{Morphos}} {ainsi
que dans le processus de sp\'{e}ciation. En ouvrant la voie \`{a} de
futures recherches, ces \'{e}tudes allant de l'\'{e}cologie \`{a} la
g\'{e}nomique des populations r\'{e}v\`{e}lent que les}
{\textit{Morphos}} ne sont pas seulement ces spectaculaires papillons
en vitrine : ils peuvent aussi nous en apprendre beaucoup sur les
processus \'{e}volutifs.
\end{altabstract}

\maketitle

\twocolumngrid

\end{noXML}

\xsection{}\unskip\noindent
The growing availability of genomic resources and next-generation
sequencing (NGS) technologies has provided insights into the genetic
and developmental basis of phenotypic diversity. Yet the evolutionary
processes ultimately responsible for such diversity are still largely
unknown. A cross-talk between different disciplines, including
developmental genetics and genomics, together with evolutionary
biology, is needed to understand how genetic and developmental
variations are shaped by neutral and selective processes driving the
course of evolution. Such cross-talk currently only occurs in a handful
of model organisms, limiting the generality of the discovered
processes. Here, by presenting recent research on \textit{Morpho}
butterfly evolution, we aim at highlighting how the study of non-model
communities of species can uncover new evolutionary processes.

\textit{Morpho} butterflies are fascinating insects encountered in the
tropical areas of central and South America~\cite{BlandinPurser2013}. A
\textit{Morpho} flying in the Amazonian forest understory is a
memorable sight, because of the peculiar iridescent blue displayed on
the dorsal sides of their wings, generating shiny flashes during
flapping flight. While these butterflies have been collected by
naturalists for more than two centuries and many taxonomists have
struggled to define the different \textit{Morpho} species 
\cite{Blandin2007}, there were surprisingly few scientific studies
investigating their ecology and evolution until recently. Nevertheless,
the large morphological and behavioural disparity of closely related
\textit{Morpho} species living within the same localities (thus defined
as sympatric species) opens multiple questions on the evolutionary
processes involved in the diversification of traits and on the effect
of ecological specialization in such diversification. Here, we aim at
summarizing current knowledge brought by research on \textit{Morpho}
butterflies, and at highlighting how these findings may open up new
research avenues in evolutionary ecology. We specifically focus on (1)
the diversification of flight behaviour throughout the vertical strata
of the forest, (2) the selective processes shaping the evolution of
their wing colour pattern and (3) the genomic and ecological factors
involved in the divergence into multiple species co-existing in
sympatry.

\section{{Adaptive evolution of flight in \textit{Morpho}}\hfil\break butterflies?}\label{sec1}

The genus \textit{Morpho} has diverged from its sister genus
\textit{Caerois} circa 38~million years ago, and contains 30 
currently-recognized species~\cite{Chazotetal2021}. The phylogenetic
relationships between species are well supported by morphological and
molecular data~\cite{Chazotetal2016,Chazotetal2021}. Most of the
species of the \textit{Morpho} genus are distributed into two main
clades, opposing species observed in two different microhabitats,
{i.e.}\ understory and canopy. Two species (\textit{Morpho eugenia} and
\textit{Morpho marcus}) belong to an outgroup that split from the rest
of the genus earlier than the divergence between the two main clades
(see phylogenetic relationships in Figure~\ref{fig2}). Such a small
phylogenetic scale is both a weakness and a strength for evolutionary
inference: on the one hand, it limits the power of phylogenetic
comparative tests, impeding the identification of the factors shaping
diversification and phenotypic evolution; on the other hand, the small
size of the group allows to aim for an exhaustive sampling in
phenotypic and genomic analyses. Most importantly, provided that enough
field investigations are conducted, a good knowledge of the ecology of
most species is in reach, allowing to identify the selective forces at
play. 

Striking morphological divergence is observed among these closely
related species (see Figure~\ref{fig1}). While all \textit{Morpho} are
large butterflies, their wingspan varies considerably among species,
from 6--7~cm for the smallest to almost 20~cm for the largest. This
morphological diversity also includes coloration: while the wings
observed in most \textit{Morpho} species are blue, some are
orange, white, or brown. Even across species displaying blue wings,
there is a marked diversity of blues, from bright to dark, shiny to
matte, and the relative extent of blue and black on the wings also
varies extensively. The disparity in wing shape is also striking in
this small butterfly genus: while the wings are short and rounded in
some species, in others they are elongated and sharp. What are the
evolutionary drivers of such stunning
morphological diversity across this small number of closely related
species? 

\begin{figure*}
\includegraphics{fig01}
\caption{\label{fig1}Male specimens of the thirty \textit{Morpho}
species illustrating the disparity in wing sizes, colours and shapes.
(A) dorsal view; (B) ventral view; columns 1--2: species observed in the
canopy; \mbox{columns~3--5:} species observed in the understory. Note the
striking contrasts between the dorsal and the ventral surfaces,
especially in species where the dorsal side is blue.}
\end{figure*}

While the ecology of most \textit{Morpho} species has been poorly
investigated so far (\cite{Debatetal2018} for a review), our
limited knowledge nevertheless suggests some effects of ecological
specialization on the morphological evolution of \textit{Morpho}. For
example,~\cite{Chazotetal2021} have suggested that adaptation to
different host plants may impact wing size evolution: the shift from
dicotyledon to monocotyledon (\textit{Chusquea} bamboo) of a small
clade of species was associated with a sharp reduction in wing size
(Figure~\ref{fig2}; see also columns A4 and B4 in Figure~\ref{fig1}). A
smaller wing size could be favoured in these species, in particular in
females that are often seen flying and ovipositing in very dense bamboo
thickets~\cite{MonteroOrtiz2010,PurserLacomme2016,
HerediaAlvarez-Lopez2005,OteroMarigo1990}; alternatively, bamboos might
constitute a poorly nutritive food, impacting development and body
size. Many observations have also reported markedly different flight
behaviours across species, opposing some species observed only high in
the canopy, with individuals performing extensive gliding phases, to
species observed mostly in the understory, with individuals relying on
flapping  flight~\cite{Devriesetal2010}. Could such vertical ecological
\mbox{stratification} within the \textit{Morpho} genus {influence} the
diversification of traits, and in particular wing shape?

\begin{figure*}
{\vspace*{-3pt}}
\includegraphics{fig02}
{\vspace*{-3pt}}
\caption{\label{fig2}Divergence of wing shape among
\textit{Morpho} species flying in contrasted
microhabitats (canopy {vs.}\ understory). The
divergence is shown by the reconstructed extreme shapes along a
canopy-understory gradient and suggests aerodynamic effects of wing
shape variations on flight performances. The orange line indicates the
shift from dicotyledon to monocotyledon host plants (bamboo),
associated with a reduction in wing size.}
{\vspace*{-3pt}}
\end{figure*}

\subsection{Evolution of wing shape across microhabitats}

The rich collections of the Paris Museum of Natural History have
enabled quantifying the wing shape of males and females from all 30
\textit{Morpho} species, using a geometric morphometric approach,
accounting for the phylogenetic relationships inferred from molecular
data~\cite{Chazotetal2016,Chazotetal2021}. This approach relies on the
position of homologous landmarks defined on wing veins and outlines,
generating a precise quantification of shape variations and a
visualization of shape differences (see Figure~\ref{fig2}). The wing
shape variation between species clearly matched the predicted
opposition between microhabitats (canopy {vs.}\ understory) and
types of flight (gliding {vs.}\ flapping): sharp triangular wing
shapes are observed in canopy species, while shorter rounded wings are
found in understory species. This morphological difference was thus
stronger than expected under a Brownian evolution model accounting for
the phylogenetic relatedness between species: this thus suggests that
the divergence in wing shape is not explained by neutral evolution only
but can also be significantly influenced by selection pressures that
differ in the canopy {vs.}\ understory microhabitats, in line
with previous \mbox{suggestions}~\cite{Devriesetal2010}. Elongated wings are
typically associated with good gliding performances, while short
rounded wings should favour manoeuvrable flapping flight, as reported
in various flying organisms (bats (e.g.~\cite{LindheNorbergetal2000}),
birds ({e.g.}~\cite{Vagasietal2016}) and butterflies ({e.g.}\ 
\cite{LeRoyetal2019})). This divergence of wing morphology might thus
reflect a behavioural adaptation to the contrasted microhabitats:
gliding might be advantageous in the open canopy, while manoeuvrability
might be favoured in the cluttered Amazonian understory. Considering
that species belonging to the outgroup clade (\textit{M.~eugenia} and
\textit{M.~marcus}) are mainly observed in the understory
(Figure~\ref{fig2}), as do species from the sister-groups
\textit{Caerois} and \textit{Antirhea}, the colonization of the canopy
is likely a secondary event, possibly impacting the evolution of flight
and related traits in these high-flying species.

\subsection{\mbox{Adaptive coevolution of wing shape and} flight}

Investigating the putative coevolution of flight behaviour and
morphology then required to combine (1) the precise characterization of
flight behaviour in both canopy and understory species to (2) the
estimation of flight performance associated with different wing shapes
using aerodynamic modelling. Field work in northern Peru allowed
recording flight data for 12 \textit{Morpho} species (eight from the
understory and four from the canopy): \textit{Morpho} were first filmed
while free flying in their natural habitat to characterize natural
flight behaviour. Using a large insectary equipped with a multicamera
videographic system then permitted to finely characterize
\textit{Morpho} flight in standardized conditions. The reconstruction
of 3D trajectories then provided estimations of a series of general
flight parameters, including speed, acceleration, sinuosity, and more
specific parameters characterizing gliding behaviour. For instance, the
position of the wings during gliding phases was measured for the
different species studied, a critical piece of information for
aerodynamic modelling. Observations in both natural and captivity
environments showed the same trends: gliding behaviour was much more
prevalent in canopy than in understory species. In turn, significantly
more powerful flapping flight was detected in understory species as
compared to understory ones. These behavioural results were used to
parametrize computational fluid dynamics (CFD) simulations. The
aerodynamic modelling showed that the wing shapes of canopy species are
associated with a higher lift-to-drag ratio, {i.e.}\ higher gliding
performances, as compared to the \mbox{aerodynamic} properties emerging from
the wing shapes of the \mbox{understory} species. This original
combination of observations of natural behaviours, quantification of
flight behaviour in captivity, and aerodynamic modelling suggests an
adaptive co-divergence of flight and wing shape across the two
microhabitats in \textit{Morpho} butterflies~\cite{LeRoyetal2021a}. But
did the microhabitat shift promote the adaptive evolution of new flight
behaviour and morphology, or was it rather facilitated by a
pre-existing variation in wing shape within the understory species?
Supporting the first hypothesis, a classic view posits that adaptive
syndromes are often initiated by behavioural shifts followed by
morphological fine-tuning~\cite{Schmalhausen1949,West-Eberhard2003}.
However, the reverse might also be true (see~\cite{Hueyetal2003}, and
\cite{Milleretal2023} for general discussions): precisely quantifying
variation in flight height and flight behaviour across species might
help solve this question.

The drivers of this vertical shift towards the canopy are also unknown.
Sexual interference, i.e.\ the occurrence of costly interspecific fights
or courtships, seems to be strong in current \textit{Morpho} species,
as suggested by experimental data  (\cite{LeRoy2021b}, see below).
Colonizing the canopy might have been advantageous, by alleviating this
competition in the understory, but the low number of species at that
time (only two; see~\cite{Chazotetal2021}) might rather point at an
{alternative}, neutral scenario. Whether this niche \mbox{partitioning} was
involved in sympatric speciation, or rather separated already formed
species is thus currently unknown and is an exciting open question.
Further diversification then took place within the canopy, filling the
new niche, and possibly prevented further secondary colonization.

The divergence of flight behaviour between canopy and understory
species might also have consequences on the evolution of coloration.
Out of the ten canopy species, seven have indeed lost the blue
iridescence and present duller colorations (Figure~\ref{fig1}),
suggesting that gliding flight might promote less conspicuous
appearance. Interestingly, flight data on \textit{Morpho rhetenor}, a
canopy species where males exhibit striking shiny iridescent-blue
coloration, revealed a powerful flapping flight, in sharp contrast with
the gliding behaviour observed in other canopy species displaying dull
colorations. These observations support an association between fast
flapping flight and blue iridescence, and suggest a complex history of
coevolution of morphological traits during the diversification of
\textit{Morpho} butterflies. 

These recent findings thus point at the cascading evolutionary effects
of interspecific interactions in sympatry: the putative competition
among \textit{Morpho} species might have favoured the colonization of
the canopy level, and the very different ecological conditions
encountered there might have released selection on flapping flight
speed and manoeuvrability and promoted the evolution of gliding flight,
imposing new selective pressures on wing size and shape, thereby also
modifying selection on wing coloration. Such coevolution of multiple
phenotypic traits, behavioural (flight) and morphological (wing shape
and colour), is a promising direction for future research. A precise
quantification of flight behaviour and flight height beyond the binary
opposition of canopy and understory, as well as a more detailed
analysis of the ecological interactions among species within
microhabitats will be necessary to identify the temporal sequence of
these phenotypic shifts and assess their causal relationships.

\begin{figure*}
\includegraphics{fig03}
{\vspace*{-1pt}}
\caption{\label{fig3}Representative examples of parallel geographic
variations of dorsal wing colour patterns observed in \textit{Morpho
helenor}, \textit{Morpho achilles} and  \textit{Morpho deidamia}, 
documented in~\cite{Llaurensetal2021}, with a schematic view of their
phylogenetic relationships. Pictures were taken in the collections of
the Natural History Museum of Paris.}
\end{figure*}

\section{\mbox{Mimicry among closely related species} \mbox{living} in
sympatry}

Several species of \textit{Morpho} display an iridescent blue colour on
the dorsal side of their wings, contrasting with a dull brownish colour
on the ventral side (\mbox{Figure~\ref{fig1}}). This dorso-ventral contrast
results in a series of flashes during flapping flight. Capture--mark
experiments carried out in the Atlantic forest of Brazil with
\textit{Morpho helenor} manipulated to display blue colours on
both wing sides show lower levels of recapture of individuals with blue
colours on both wing sides, as compared to wild-type ones displaying
iridescent blue only on the dorsal side~\cite{Vieira-Silvaetal2024}.
This suggests a positive influence of the dorsal-ventral
contrast producing flash effects during flight on the survival of
iridescent blue \textit{Morphos}. The visual effect of the
contrasted dorso-ventral contrast associated with an erratic flight is
indeed likely to enhance the difficulty of predators in capturing them.
\cite{Murali2018} then tested the ability of humans to catch a moving
stimulus, comparing a situation where the stimulus was visually
constant to a situation where it varied in colour while moving. This
experiment showed that the colour change during the movement was
associated with decreased attack success as compared to white or
background matching stimuli. This experiment is thus consistent with
the hypothesis of an effect of the peculiar dorso-ventral pattern of
\textit{Morpho} butterflies in limiting predation. Furthermore,
this specific colour pattern may also act as a signal of escape ability
and hence deter predators from chasing butterflies displaying such
coloration. This hypothesis was suggested by  \cite{Pinheiroetal2016},
and experiments carried out with wild birds were generally consistent
with his hypothesis~\cite{PinheiroCampos2019}: \textit{Morpho}
butterflies were sight-rejected 11 out of 13 times by wild jacamar
birds while flying. Although these experiments were based on a limited
sample size, they suggest that predators may (1) recognize and avoid
butterflies displaying the contrasted blue signal and (2) consume these
butterflies, therefore confirming their palatability. These
observations suggest that the evolution of blue colour patterns in
\textit{Morpho} butterflies could be influenced by bird cognitive
capacities: in a given locality, colour patterns commonly displayed by
evasive prey would be recognized and avoided by local birds. Such
predator behaviour likely favours positive selection of colour patterns
commonly displayed by evasive prey, therefore promoting evolutionary
convergence in colour patterns in sympatric prey species. Such
evolutionary convergence in colour patterns has been confirmed multiple
times in toxic species, including butterflies ({i.e.}\ 
M\"{u}llerian mimicry,~\cite{Sherratt2008}). Convergence in colour
patterns could then be \mbox{promoted} by selection from the local communities
of birds~\cite{Pinheiroetal2016}. In an experiment in controlled
conditions, Paez et~al.~\cite{Paez2021} indeed showed that blue tits can
associate a colour pattern with evasive capacities. Comparing the
learning curve of birds when associating the same colour pattern with
either a distasteful experience or an evasive experience showed that
birds tended to learn the colour pattern faster when associated with
evasive prey. The lack of success of the birds in catching the prey is
thus likely to trigger a faster learning response as compared to
unpalatability. The speed of colour-pattern learning by birds likely
contributes to the strength of selection: the faster each bird does
learn in the wild, the lower the risk there is for a given butterfly to
encounter a bird that would be unaware of the difficulty of capture
associated with the visual signal. The fast learning speed of birds
facing evasive prey may therefore provide a very strong advantage to
mimetic coloration in prey with high escaping skills. 

Consistent with this hypothesis, we recently demonstrated a striking
parallelism in the phenotypic diversification of three blue
\textit{Morpho} species throughout their sympatric distribution
(Figure~\ref{fig3}). Using samples of the closely related species
\textit{Morpho achilles}, \textit{M.~helenor} and
\textit{Morpho deidamia} from the collections of the Natural
History Museum in Paris (France), we quantified the variations in black
and blue dorsal wing patterns displayed in individuals collected
throughout the geographic range of the three species. Using permutation
tests, we showed that pairwise phenotypic distances between individuals
from different species were significantly more similar within
geographic localities, as compared to between localities. The high
resemblance between species within localities is likely resulting from
multiple local convergence in the width of their dorsal blue band
\cite{Llaurensetal2021}. The effect of predation on the
evolution of resemblance is currently the most likely hypothesis, but
it has not been directly tested yet, so that we cannot rule out the
effect of contrasted selective regimes occurring in different
geographic localities. Interestingly, evidence for evasive mimicry is
currently still scarce, but this phenomenon is probably more important
for the evolution of coloration than previously acknowledged. On top of
butterflies~\cite{PinheiroandFreitas2014}, evasive mimicry has indeed been
hypothesized in various prey taxa, including beetles~\cite{Guerra2019},
\mbox{grasshoppers}~\cite{Balgooyen1997} and flies, and may involve various
predators from birds to mantids~\cite{Loeffler-HenrySherratt2024}. The
colours displayed by the evasive prey are likely conspicuous, allowing
recognition by potential predators in a similar manner as in
M\"{u}llerian mimicry. However, the iridescent blue of the wings in
\textit{Morpho} butterflies likely directly contributes to the
difficulty of capture, not only because of the dorso-ventral contrast,
but also because of the unstable visual appearance of the iridescent
surface, possibly enhancing predator confusion. The evolution of the
colour pattern might thus be constrained by the direct survival
advantage provided by the visual effects generated during escape
flight. Differences in colour pattern among species might be blurred by
motion, as the blue dorsal side is only visible during flight, possibly
reducing the strength of selection on minute details of the colour
pattern. In sharp discrepancy with this hypothesis, the very close
similarity between \textit{M.~achilles} and \textit{M.~helenor}
suggests that this potential blurring does not limit the
precision of the convergence. Alternatively, their close phylogenetic
proximity might impose a tight parallelism due to genetic and
developmental constraints. Interestingly, the more distant but also
convergent species \textit{M.~deidamia} displays a slightly
different colour pattern suggesting an effect of phylogenetic distances
constraining the level of resemblance, and consistent with the motion
blurring effect allowing imperfect mimicry.

Recent findings on the evolution of colour pattern in Morpho butterfly
communities shed light on the potential significance of evasive mimicry
in shaping the joint evolution of dorso-ventral coloration and flight
behaviour: how did these evasive syndromes evolve? Does divergence in
flight morphology and behaviour evolve before changes in coloration, or
the other way around? It also raises new questions on the parallel
evolution of colour patterns in closely related species: are similar
molecular pathways involved in these multiple convergence events, or
alternatively does introgression between closely related species
facilitate such parallelism?

\section{Reproductive interferences and evolution of circadian
activities}

Mimicry among butterflies frequently occurs among distantly related
species \cite{VanZandtBrower1957,Beccaloni1997}. Precise quantification
of phenotypic distances in Papilionidae \mbox{butterflies} recently suggested
that mimicry might be more prevalent in distantly related species
rather than closely related ones, especially in 
males~\cite{Puissantetal2023}. This pattern may be due to the opposite effect
of natural and sexual selection, since the wing colour pattern is also
involved in mate recognition~\cite{Jigginsetal2001}: the evolution of
colour patterns in sympatric species could indeed be influenced by
predation favouring convergence in toxic or evasive prey, but also by
sexual selection favouring divergence in closely related species,
because of the costs associated with heterospecific interactions, such
as heterospecific mating or rivalry for instance 
(see~\cite{GroningHochkirch2008} for a review on heterospecific behavioural
interactions generating reproductive interferences across animal
species). Convergence in wing colour patterns could thus be more likely
to happen across distantly-related species, where multiple alternative
pre-mating barriers have already accumulated. In  \textit{Morpho}
butterflies, however, we documented striking resemblance in 
patterns~\cite{Llaurensetal2021}, as well as iridescent blue
\cite{Ledamoiseletal2025} within locality, among the closely-related
species \textit{M.~achilles} and \textit{M.~helenor}. Because
iridescent coloration has been shown to be involved in mate choice in
other animals~\cite{DoucetMeadows2009}, the dorsal colour pattern
displayed in \textit{Morpho} could have an effect on sexual attraction
and may result in heterospecific interactions. Using solar-powered
mobile dummy butterflies placed in a field site in Amazonian Peru, we
found that wild males of all these three species were attracted to the
blue colour of dummies outfitted with wings from all these three
different  species~\cite{LeRoy2021b}. The interactions between wild
males patrolling in the field and the dummies provide evidence of an
enhanced attraction toward the locally displayed colour pattern as
compared to patterns displayed in other localities. Wild males were
thus attracted by the local colour patterns of males and females from
the three species, suggesting intense heterospecific male--male
competition and courtship. Behavioural experiments in cages also
confirmed the lack of visual discrimination of conspecific {vs.}\ 
heterospecific females by wild males from two sister species,
\textit{M.~achilles} and \textit{M.~helenor} 
\cite{Ledamoiseletal2025}.

Nevertheless, sequencing individuals of the two sister-species
\textit{M.~achilles} and \textit{M.~helenor} sampled in the same
locality in Peru allowed to reconstruct the history of gene flow
between these sympatric species. Demographic inference models based on
these \mbox{genomic} variations within and between species are consistent with
current genetic isolation~\cite{LeRoy2021b}. This suggests that pre- or
post-zygotic mechanisms might prevent gene flow between these two
species, despite limitations in species recognition based on
coloration. Interestingly, capture/mark/recapture experiments carried
out in the same Peruvian locality revealed that males from these two
mimetic species patrol at different times of the 
day~\cite{LeRoy2021b}. This divergent temporal window may favour the
evolution of divergent temporal niches, if male behaviour is consistent
with variations in female mating availability during the day. In those
species, female behaviour makes them less likely to be observed because
they are typically found deeper in the understory, close to their host
plants, while males patrol along river beds. Males transfer
spermatophores to females during mating, and these spermatophores can
provide sperm to fertilize multiple eggs and usually prevent successive
matings with other males. Females are thus probably only mating rarely
throughout their life, while males are probably able to mate multiple
times. The availability of virgin females is thus probably the limiting
factor shaping the reproductive success of males, so that variation in
the timing of adult emergence could shape the temporal niche of
reproductive activities in these species. Using a theoretical model,
\cite{Bouinieretal2024} indeed showed that male--male competition to
access virgin females can promote the divergent evolution of temporal
niches in sympatry. A similar effect has also been hypothesized to
contribute to allochronic speciation in \textit{Spodoptera} moths
\cite{vanDoornetal2025}. Such a process could be further promoted by
genetic incompatibilities evolving within populations.\looseness=-1

Allochrony (differences in breeding time) is generally suggested to be
an important pre-zygotic mechanism promoting speciation, or evolving as
a trait reinforcing barrier to gene flow between recently diverged
species secondary getting in contact~\cite{TaylorandFriesen2017}.
Seasonal variations in phenology are documented as a mechanism involved
in sympatric speciation, especially in 
plants~\cite{DevauxLande2008,GaudinierBlackman2020}.  However, daily
variation in reproductive timing is much less documented except for
some insects, such as \textit{Drosophila}~\cite{SakaiIshida2001} or
some Lepidoptera~\cite{Hannigeretal2017}. In neotropical skipper
butterflies, for instance, observations of more than 400 species from
different genera show significant differences in flight time between
males of closely related species~\cite{Devriesetal2008}. In butterflies
and other insects, daily activity is controlled by a series of genes
and transcription factors that regulate the circadian clock 
\cite{Bradyetal2021}. Circadian genes, as \textit{vrille} or
\textit{period}, have been suggested to control breeding time in moth
species as \textit{Spodoptera frugiperda} or \textit{Plutella
xylostella}. In the case of \textit{S.~frugiperda}, the gene
\textit{vrille} could be responsible for the pre-zygotic isolation of
the two strains of the species, as the differential transcription of
the gene is associated to the allochronic differentiation of the two
strains~\cite{Hannigeretal2017,Wangetal2023}. The sequencing and
annotation of reference genomes for eleven \textit{Morpho} species
recently allowed to study the evolution of eight circadian genes
throughout the \textit{Morpho} genus~\cite{LopezVillavicencioetal2024}.
Signal of positive selection was detected in the circadian gene
\textit{period}, suggesting that this gene could be acting in the
diversification of flight time in this genus.\looseness=-1

By highlighting the divergence in temporal niches and putative genetic
bases for the evolution of daily allochrony in Morpho butterflies,
recent studies show the significance of the diel niche in the
diversification of ecological niches, specifically in communities where
multiple closely related species co-occur in sympatry, as in tropical
areas. It also calls for further research on the biotic and abiotic
factors shaping these daily temporal niches, as well as on the
respective contributions of genetic and developmental effects to such
divergence in circadian activities.\looseness=-1

{\vspace*{-2pt}}

\section{{Genomic barriers to gene flow and}\hfil\break Z-chromosome evolution}

{\vspace*{-2pt}}

\subsection{Reduced gene flow in sympatry despite mimicry}

{\vspace*{-2pt}}

Other mechanisms acting at the post-zygotic stage can also prevent gene
flow and promote speciation between closely related species in
sympatry. These mechanisms occur post-fertilization, resulting in the
production of hybrid zygotes with lower viability or fitness compared
to non-hybrid zygotes. Chromosomal rearrangements, such as inversions,
may serve as post-zygotic barriers by reducing recombination in the
inverted regions, thereby fuelling divergence between haplotypes and
contributing to reproductive  isolation~\cite{KirkpatrickBarton2006}.
Inversions are common across various biological groups, including
insects, teleosts, birds, and
mammals~\cite{WellenreutherBernatchez2018}.

In some groups, inversions tend to accumulate more on sex chromosomes
compared to autosomes. For instance, a study of 411 passerine bird
species found a higher probability of fixation for inversions on the Z
chromosome than on the autosomes~\cite{HooperPrice2017}. Sister species
with overlapping ranges were also more likely to exhibit inversions in
their genome than those in allopatry, suggesting an effect of the
reinforcement process in favouring inversions between sympatric
species~\cite{HooperPrice2017}. Similarly, in the genus
\textit{Morpho}, comparisons between species pairs revealed extensive
chromosomal rearrangements in the Z contig compared to the autosomes,
especially between closely related species coexisting in sympatry and
with overlapping temporal niches~\cite{LopezVillavicencioetal2024}.

\subsection{Effect of the inversions and gene evolution in the Z
chromosome}

In species with chromosomal sex determination, it has usually been
observed that loci harboured on sex chromosomes may evolve faster than
similar loci on the autosomes~\cite{Charlesworthetal1987}, a phenomenon
commonly known as faster-X or faster-Z 
evolution~\cite{Charlesworthetal1987,VicosoCharlesworth2006}. 
Traditionally, the faster Z or X effect has been attributed to the
faster fixation of beneficial alleles by positive selection, because of
immediate expression at the hemizygotic
stage~\cite{Charlesworthetal1987}. In autosomes, loci with recessive
effects are not exposed to selection because they are masked by the
dominant ancestral allele. However, if these loci arise on the X or Z
chromosome, their effects on fitness are fully expressed in the
hemizygous sex (the sex with only one copy of the sex chromosome, such
as males in species with XY sex determination or females in ZW 
systems)~\cite{VicosoCharlesworth2006}. Then, recessive beneficial
alleles will be more rapidly fixed by positive selection when they are
located on the X or Z chromosome. However, the faster evolution of X/Z
chromosomes can also result from the effects of genetic drift, which
limit the purging of deleterious mutations. In each mating pair, there
are four copies of autosomal genes but only three copies of X or
Z-linked genes. Consequently, the effective population size ($N_{\mathrm{e}}$) for
X or Z sex chromosomes is reduced compared to autosomes (3/4 $N_{\mathrm{e}}$).
This reduced $N_{\mathrm{e}}$ may limit the elimination of slightly deleterious
mutations within each species.

Empirically, a faster evolution of the X/Z chromosome has been observed
in many groups with XY and ZW determination such as mammals, birds,
butterflies, snakes, spiders, or the salmon louse
\textit{{Lepeophtheirus} salmonis}~\cite{Bechsgaardetal2019,Irwin2018,Manketal2009,MongueKawahara2022,Mongue2023,Sacktonetal2014,TorgersonSingh2006,Vicosoetal2013,Wrightetal2015}. 
The frequent occurrence of faster evolution of X/Z chromosomes suggests
that they substantially contribute to key evolutionary processes such
as speciation and adaptation.

In the case of \textit{Morpho}, we analyzed the selective pressures
acting on the genes located on the Z chromosomes and in the autosomes
among 12 assembled genomes belonging to 11 species. We specifically
compared the ratio of non-synonymous {vs.}\ synonymous mutations
($\mathrm{d}N/\mathrm{d}S$) on the genes located in the autosomes and
the genes located on the Z chromosome. We detected faster evolution for
genes in the Z contig compared to the autosomes, suggesting a potential
role of the Z chromosome in driving adaptive evolution in this group.
The faster evolution of genes located on the Z chromosome was also
confirmed when comparing closely {related} species pairs. We found
significant differences in the $\mathrm{d}N/\mathrm{d}S$ ratio between
autosomal genes and Z-linked genes, with Z-linked genes showing higher
average values than autosomal genes. This pattern was especially
pronounced in species pairs that share the same habitat and have
overlapping flight periods~\cite{LopezVillavicencioetal2024}. This
suggests that divergent selection among sympatric species and/or
reinforcement processes could contribute to the faster evolution of the
Z chromosome among sympatric species.

Although our genomic analyses revealed a highly dynamic Z chromosome,
characterized by the presence of inversions and an elevated 
$\mathrm{d}N/\mathrm{d}S$
ratio, it is crucial to corroborate these findings at the population
level. Population genomic analyses can determine whether these
inversions are fixed in different populations of the species where they
were initially identified. Additionally, such analyses can shed light
on the roles of Z-linked genes in speciation and adaptation.
Investigating the selective pressures on these genes in closely related
species, particularly in contexts of sympatry and allopatry, would
provide valuable insights into their evolutionary significance.

\section{Conclusions}

\textit{Morpho} butterflies have long been considered for their beauty
rather their scientific interest, resulting in a paradoxical situation:
they are heavily collected and sold, but their biology and ecology are
poorly known. The recent works reviewed here {suggest} that
\textit{Morphos} are ideally suited to allow investigating {fundamental}
questions of evolutionary \mbox{biology}. \mbox{Focusing} on wild communities of
closely related species is indeed a relevant way to identify key
mechanisms involved in speciation, ecological specialization, as well
as diversification of adaptive traits. The results obtained on
\textit{Morpho} butterflies highlight the relevance of combining
investigations on the phenotypic, genomic and ecological variations in
non-model organisms to shed light on the evolutionary mechanisms
generating and maintaining natural communities in the wild.

\section*{Declaration of interests}
Views and opinions expressed are those of the authors only and do not
necessarily reflect those of the European Union or the European
Research Council. Neither the European Union nor the granting authority
can be held responsible for them.

\section*{Funding}
The work of VL and her team is currently funded by the European Union
(ERC Consolidator grant OUTOFTHEBLUE, project number 101088089). 

\CDRGrant[ERC]{101088089}

\back{}

\printbibliography
\refinput{crbiol20240768-reference.tex}

\end{document}
</pre></body></html>