Biology subjects

Smadi, C.

Publications and source records attributed to Smadi, C..

8 recordsLinked to original sources

bioRxiv2024

Evolution of divergent daily temporal niches shaped by male-male competition can generate sympatric speciation

Specialisation into different ecological niches is assumed as an important driver of speciation in sympatry. Here we focused on male-male competition fuelling population divergence, without assuming any ecological specialisation. We investigated how antagonistic interactions between males can promote divergent evolution of timings of reproductive activities during the day, as observed in some closely-related insect species living in sympatry. We used a multi-locus, comprehensive stochastic model to investigate the evolution of (1) the timing of reproductive activity as a quantitative trait and (2) neutral loci that may generate genetic incompatibilities among divergent individuals. We specifically explore how male-male competition for female access can generate negative frequency-dependence on the timing of reproductive activities and fuel population divergence. Our simulations in finite populations highlight the strong effect of male-male competition and operational sex-ratio on the evolution of divergent temporal niches. They also show how genetic incompatibilities promote the differentiation among populations with divergent temporal niches, but may also impair their co-existence. Our model therefore highlights male-male competition as an important factor shaping the evolution of diel niches, that may fuel sympatric speciation.

evolutionary biology↗

bioRxiv2022

How many cues are sexy? Evolution of mate preference towards multiple traits in sympatric species

Mate preferences may target traits (1) enhancing offspring adaptation and (2) reducing heterospecific matings. Because similar selective pressures are acting on traits shared by different sympatric species, preference enhancing offspring adaptation may increase heterospecific mating, in sharp contrast with the classical case of so-called magic traits. Using a mathematical model, we study which and how many traits will be used during mate choice, when preferences for locally adapted traits increase heterospecific mating. In particular, we study the evolution of preference towards an adaptive vs. a neutral trait in sympatric species. We take into account sensory trade-offs which may limit the emergence of preference for several traits. Our model highlights that the evolution of preference towards adaptive vs. neutral traits depends on the selective regimes acting on traits but also on heterospecific interactions. When the costs of heterospecific interactions are high, mate preference is likely to target neutral traits that become a reliable cue limiting heterospecific matings. We show that the evolution of preference towards a neutral trait benefits from a positive feedback loop: the more preference targets the neutral trait, the more it becomes a reliable cue for species recognition. We then reveal the key role of sensory trade-offs and the cost of choosiness favouring the evolution of preferences targeting adaptive traits, rather than traits reducing heterospecific mating. When sensory trade-offs and the cost of choosiness are low, we also show that preferences targeting multiple traits evolve, improving offspring fitness by both transmitting adapted alleles and reducing heterospecific mating. Altogether, our model aims at reconciling good gene and reinforcement models to provide general predictions on the evolution of mate preferences within natural communities. Impact SummaryMate preferences are widespread throughout the animal kingdom and generate powerful selective forces impacting the diversification of traits and species. The evolution of such preferences has been the focus of multiple theoretical and empirical studies and intense scientific debates. The evolution of mate preference (1) enhancing offspring fitness and (2) reducing heterospecific mating have been mostly studied separately, except in the specific case of preference for so-called magic traits that increase both offspring survival and species divergence. However, in many cases, the evolution of traits in sympatric species generates conflicting evolutionary forces acting on preferences. On one hand, enhanced offspring survival promotes preference towards locally adaptive traits and may thus lead to convergent evolution of traits among sympatric species. On the other hand, the evolution of similar traits in sympatric species may generate costly heterospecific sexual interactions promoting preference towards traits that diverge between species. Here, we thus build a general mathematical model to investigate the evolutionary factors determining which and how many traits are targeted by mate choice. We especially determine whether preferences will likely target adaptive vs. neutral traits. Our model highlights that the evolution of preferences for adaptive vs. neutral traits in sympatric species depends on within-species mating opportunities but also on the niche overlap between species, tuning heterospecific interactions. By jointly considering (1) the selection regimes acting on the targeted traits within species, as well as (2) interactions with other species living in sympatry, our theoretical study provides a general framework reconciling these research fields.

evolutionary biology↗

bioRxiv2022

Origin and persistence of polymorphism in loci targeted by disassortative preference: a general model

The emergence and persistence of polymorphism within populations generally requires specific selective regimes. Here, we develop an unifying theoretical framework to explore how disassortative mating can generate and maintain polymorphism at the targeted loci. To this aim, we model the dynamics of alleles at a single locus A in a population of haploid individuals, where reproductive success depends on the combination of alleles carried by the parents at locus A. Our theoretical study of the model confirms that the conditions for the persistence of a given level of allelic polymorphism depend on the relative reproductive advantages among pairs of individuals. Interestingly, equilibria with unbalanced allelic frequencies were shown to emerge from successive introduction of mutants.We then investigate the role of the function linking allelic divergence to reproductive advantage on the evolutionary fate of alleles within population. Our results highlight the significance of the shape of this function on both the number of alleles maintained and their level of genetic divergence. Large number of alleles are maintained with substantial turn-over among alleles when disassortative advantage slowly increases when allelic differentiation becomes large. In contrast, few highly differentiated alleles are predicted to be maintained when genetic differentiation has a strong effect on disassortative advantage. These opposite effects predicted by our model shed light on the levels of allelic differentiation and polymorphism empirically observed in loci targeted by disassortative mate choice.

evolutionary biology↗

bioRxiv2022

How does the host community structure affect the epidemiological dynamics of emerging infectious diseases?

Many pathogens, especially those responsible for emerging infectious diseases, are transmitted in a host community. How the host community structure affects an epidemic is still debated, particularly whether increasing the host community complexity would tend to amplify or dilute the incidence of an epidemic in a target population, e.g. humans or cattle. In this paper, we build a stochastic SIR model and compare epidemiological dynamics in a target population between three simple host community structures with an increasing complexity. Globally, our results show two possible main outcomes. First, an intermediate host can have a diluting effect by preventing the direct transmission from hosts to the target population, thus reducing the prevalence of infection. Second, when two sources of infection are considered, the effects of the epidemic are generally amplified. By highlighting that the structure of the ecological hosts network can dramatically affect epidemics, our results may have implications for the control of emerging infectious diseases.

ecology↗

bioRxiv2021

Evolutionary origins of sexual dimorphism : Lessons from female-limited mimicry in butterflies.

The striking female-limited mimicry observed in some butterfly species is a text-book example of sexually-dimorphic trait submitted to intense natural selection. Two main evolutionary hypotheses, based on natural and sexual selection respectively, have been proposed. Predation pressure favouring mimicry toward defended species could be higher in females because of their slower flight, and thus overcome developmental constraints favouring the ancestral trait that limits the evolution of mimicry in males but not in females. Alternatively, the evolution of mimicry in males could be limited by females preference for non-mimetic males. However, the evolutionary origin of female preference for non-mimetic males remains unclear. Here, we hypothesise that costly sexual interactions between individuals from distinct sympatric species might intensify because of mimicry, therefore promoting female preference for non-mimetic trait. Using a mathematical model, we compare the evolution of female-limited mimicry when assuming either alternative selective hypotheses. We show that the patterns of divergence of male and female trait from the ancestral traits can differ between these selection regimes. We specifically highlight that divergence in females trait is not a signature of the effect of natural selection. Our results also evidence why female-limited mimicry is more frequently observed in Batesian mimics.

evolutionary biology↗

bioRxiv2021

The limits of evolutionary convergence in sympatry: reproductive interference and developmental constraints leading to local diversity in aposematic signals

Mutualistic interactions between defended species represent a striking case of evolutionary convergence in sympatry, driven by the increased protection against predators brought by mimicry in warning traits. However, such convergence is often limited: sympatric defended species frequently display different or imperfectly similar warning traits. The phylogenetic distance between sympatric species may indeed prevent evolution towards the exact same signal. Moreover, warning traits are also involved in mate recognition, so that trait convergence might result in heterospecific courtship and mating. Here, we develop a mathematical model to investigate the strength and direction of evolution of warning trait in defended species with different ancestral traits. Specifically, we determine the effect of phenotypic distances between ancestral trait states of sympatric defended species and of costs of heterospecific sexual interactions on imperfect mimicry and trait divergence. Our analytical results confirm that reproductive interference and historical constraints limit the convergence of warning traits, leading to either complete divergence, or imperfect mimicry. Our model reveals that imperfect mimicry evolves only when ancestral trait values differ between species due to historical constraints and highlights the importance of female and predator discriminations in the evolution of such imperfect mimicry. Our study thus provides new predictions on how reproductive interference interacts with historical constraints and may promote the emergence of novel warning traits, enhancing mimetic diversity.

evolutionary biology↗

bioRxiv2020

When do opposites attract? A model uncovering the evolution of disassortative mating

Disassortative mating is a rare form of mate preference that promotes the persistence of polymorphism. While the evolution of assortative mating, and its consequences on trait variation and speciation have been extensively studied, the conditions enabling the evolution of disassortative mating are still poorly understood. Mate preferences increase the risk of missing mating opportunities, a cost that can be compensated by a greater fitness of offspring. Heterozygote advantage should therefore promote the evolution of disassortative mating, which maximizes the number of heterozygous offspring. From the analysis of a two-locus diploid model, with one locus controlling the mating cue under viability selection and the other locus coding for the level of disassortative preference, we show that heterozygote advantage and negative frequency-dependent viability selection acting at the cue locus promote the fixation of disassortative preferences. The conditions predicted to enable the evolution of disassortative mating in our model match the selection regimes acting on traits subject to disassortative mating behavior in the wild. In sharp contrast with the evolution of assortative preferences, we also show that disassortative mating generates a negative frequency-dependent sexual selection, which in turn disadvantages heterozygotes at the cue locus, limiting the evolution of disassortative preferences. This negative feedback loop could explain why this behavior is rare in natural populations.

evolutionary biology↗

bioRxiv2017

Stochastic dynamics of an epidemics with recurrent spillovers from an endemic reservoir

Most emerging human infectious diseases have an animal origin. Yet, while zoonotic diseases originate from a primary reservoir, most theoretical studies have principally focused on single-host processes, either exclusively humans or exclusively animals, without considering the importance of animal to human transmission for understanding the dynamics of emerging infectious diseases. Here we aim to investigate the importance of spillover transmission for explaining the number and the size of outbreaks. We propose a simple stochastic Susceptible-Infected-Recovered model with a recurrent infection of an incidental host from a reservoir (e.g. humans by a zoonotic species), considering two modes of transmission, (1) animal-to-human and (2) human-to-human. The model assumes that (i) epidemiological processes are faster than other processes such as demographics or pathogen evolution and (ii) that an epidemic occurs until there are no susceptible individuals left. The results show that during an epidemic, even when the pathogens are barely contagious, multiple outbreaks are observed due to spillover transmission. Overall, the findings demonstrate that the only consideration of direct transmission between individuals is not sufficient to explain the dynamics of zoonotic pathogens in an incidental host.

epidemiology↗