Predation as a driver of reproductive isolation - from adaptive divergence to hybrid inviability

Natural selection can play an important role in the origin of new species. When reproductive isolation evolves as a result of ecologically-based divergent natural selection, the process is referred to as ecological speciation. In most organisms, sufficient reproductive isolation is considered to be essential for the establishment of new species. However, reproductive isolation typically involves multiple isolating barriers, and we still lack knowledge of how some barriers are affected by the level of ecological divergence and the stage of speciation. The aim of this thesis is to estimate how a potent source of ecological selection, predation, may drive reproductive isolation. First, I study multiple isolated populations of Bahamas mosquitofish (Gambusia hubbsi), that have adapted to either of two distinct selective regimes depending on the presence or absence of predatory fish. I estimate how the behaviour of mosquitofish has diverged under these contrasting predation regimes, and whether reproductive isolation has evolved to be stronger between populations from different predation regimes. Second, I study the behavioural phenotype of naturally occurring hybrids between roach (Rutilus rutilus) and common bream (Abramis brama), and ask if maladaptive behaviour can underlie increased susceptibility to predation in hybrids. Through behavioural trials using either wild-caught or laboratory-reared Bahamas mosquitofish, I show that key behavioural traits have diverged between predation regimes, but also highlight that the degree of divergence is often sex specific. I found that low-predation environments may select for foraging traits that are likely beneficial under high resource competition, but this effect was only seen in the female sex. I also show that male, but not female, mating behaviours have diverged between predation regimes, as males adapted to a high-predation regime courted females and attempted to initiate mating more actively in comparison to males originating from low-predation environments. By comparing behavioural traits expressed during within-population and between-population mating trials, I discovered that females were more aggressive towards foreign males and initiated aggression faster towards males from the opposite predation regime. I thus show that ecological adaptation may act to strengthen behavioural isolation between populations in this system. Furthermore, I show that hybrids produced between parents originating from different predation regimes have the lowest survival rates out of all hybrids and pure-line offspring reared in common-garden conditions. This indicates that ecological divergence can lead to intrinsic hybrid incompatibilities relatively early along the speciation continuum. The hybrid crosses between different predation regimes also showed intermediate fast-start escape-performance abilities when compared to crosses within the same predation regime, indicating that hybrids produced between divergently adapted populations may have lower ecological viability in the high-predation environment. Monitoring of the migration patterns through passive telemetry revealed that roach × bream hybrids show a higher frequency of migratory trips between the stream and lake habitats, a behaviour that exposes them to a higher predation risk. I thus show that predation can reinforce species integrity by selecting against hybrid phenotypes.In summary, differences in predation risk between populations can lead to stronger reproductive isolation as a by-product of adaptive divergence. Furthermore, several forms of pre- and postzygotic isolation may be important for this process, even at an early stage of speciation. Finally, predation may also play an important role in the later stages of speciation as a reinforcer of species integrity

Data for experiment 1 & 2

This zip-file contains three separate data files including original data collected for the two experiments: Experiment 1: male nest choice, experiment 2: Female nest and partner choice. files: 01_MaleChoice.txt, 01b_MaleChoiceConsistency.txt, 02_FemaleChoice.txt. The first line contains column headers with descriptions of the variables. See publication for more details, selection of relevant variables, and data handling

Maladaptive migration behaviour in hybrids links to predator-mediated ecological selection

Different migratory species have evolved distinct migratory characteristics that improve fitness in their particular ecological niches. However, when such species hybridize, migratory traits from parental species can combine maladaptively and cause hybrids to fall between parental fitness peaks, with potential consequences for hybrid viability and species integrity. Here, we take advantage of a natural cross-breeding incident to study migratory behaviour in naturally occurring hybrids as well as in their parental species and explore links between migratory traits and predation risk. To achieve this, we used electronic tags and passive telemetry to record detailed individual migration patterns (timing and number of migratory trips) in two common freshwater fish species, roach Rutilus rutilus, common bream Abramis brama as well as their hybrids. Next, we scanned for tags regurgitated by a key avian predator (great cormorant Phalacrocorax carbo) at nearby roosting sites, allowing us to directly link migratory behaviour to predation risk in the wild. We found that hybrid individuals showed a higher number of short, multi-trip movements between lake and stream habitats as compared to both parental species. The mean date of first lake departure differed between bream and roach by more than 10 days, while hybrids departed in two distinct peaks that overlapped with the parental species' averages. Moreover, the probability of cormorant predation increased with multi-trip movement frequency across species and was higher for hybrids. Our data provide novel insights into hybrid viability, with links to predator-mediated ecological selection. Increased exposure to predators via maladaptive migratory behaviour reduces hybrid survival and can thereby reinforce species integrity

Turbidity data

Raw data and the script to determine how similar the UV threat will be across the three selected blue holes

Variation in predation regime drives sex-specific differences in mosquitofish foraging behaviour

Predation is a well-studied driver of ecological selection on prey traits, which frequently drives divergence in anti-predator performance across environments that vary in predation risk. However, predation also alters prey mortality regimes, where low predation risk often results in higher prey densities and consequently higher intensities of intraspecific resource competition. In addition, predation risk alters the foraging context, as acquiring food can be risky in the presence of predators. Thus, different predation regimes can drive divergent selection on traits associated with resource competition, such as foraging behaviours. Moreover, because sexes often differ in susceptibility to predation and limitations to their reproductive output, the intensity of the tradeoff between predator avoidance and resource competition may depend on sex. We used a laboratory experiment to assess key aspects of foraging performance in a predator-free context in Bahamas mosquitofish Gambusia hubbsi wild-caught from multiple populations that experience either high or low levels of predation risk. When competing for limited food resources at a common density, females from low-predation regimes showed higher foraging and food consumption rates than females from high-predation regimes. Males showed fewer differences between predation regimes, and an opposite pattern from females. We suggest these sex-specific effects result from females facing a greater tradeoff between predation risk and resource competition, combined with males from high-predation environments elevating foraging behaviours in the absence of nearby predators and females. Females of this species are larger than males, bear live young and show higher foraging rates in the wild than males. On the other hand, males spend more time pursuing females in the wild, and may exhibit greater flexibility in foraging behaviours based on the immediate context. Our results show that varying levels of predation risk can lead to differences in behaviours associated with resource competition, but these effects can strongly differ between sexes. CC BY 3.0First published: 16 March 2021</p

Toward the integration of speciation research

Acknowledgements: We thank the staff of the Tvärminne Zoological Station (University of Helsinki) for their hospitality during the workshop. We are also grateful to everyone who applied to attend the workshop.Funder: European Society for Evolutionary Biology; DOI: https://doi.org/10.13039/501100013632Abstract Speciation research—the scientific field focused on understanding the origin and diversity of species—has a long and complex history. While relevant to one another, the specific goals and activities of speciation researchers are highly diverse, and scattered across a collection of different perspectives. Thus, our understanding of speciation will benefit from efforts to bridge scientific findings and the diverse people who do the work. In this paper, we outline two ways of integrating speciation research: (i) scientific integration, through the bringing together of ideas, data, and approaches; and (ii) social integration, by creating ways for a diversity of researchers to participate in the scientific process. We then discuss five challenges to integration: (i) the multidisciplinary nature of speciation research, (ii) the complex language of speciation; (iii) a bias toward certain study systems; (iv) the challenges of working across scales; and (v) inconsistent measures and reporting standards. We provide practical steps that individuals and groups can take to help overcome these challenges, and argue that integration is a team effort in which we all have a role to play.</jats:p

Toward the integration of speciation research

International audienceSpeciation research—the scientific field focused on understanding the origin and diversity of species—has a long and complex history. While relevant to one another, the specific goals and activities of speciation researchers are highly diverse, and scattered across a collection of different perspectives. Thus, our understanding of speciation will benefit from efforts to bridge scientific findings and the diverse people who do the work. In this paper, we outline two ways of integrating speciation research: (i) scientific integration, through the bringing together of ideas, data, and approaches; and (ii) social integration, by creating ways for a diversity of researchers to participate in the scientific process. We then discuss five challenges to integration: (i) the multidisciplinary nature of speciation research, (ii) the complex language of speciation; (iii) a bias toward certain study systems; (iv) the challenges of working across scales; and (v) inconsistent measures and reporting standards. We provide practical steps that individuals and groups can take to help overcome these challenges and argue that integration is a team effort in which we all have a role to play

Toward the integration of speciation research

Acknowledgements: We thank the staff of the Tvärminne Zoological Station (University of Helsinki) for their hospitality during the workshop. We are also grateful to everyone who applied to attend the workshop.Funder: European Society for Evolutionary Biology; DOI: https://doi.org/10.13039/501100013632Speciation research—the scientific field focused on understanding the origin and diversity of species—has a long and complex history. While relevant to one another, the specific goals and activities of speciation researchers are highly diverse, and scattered across a collection of different perspectives. Thus, our understanding of speciation will benefit from efforts to bridge scientific findings and the diverse people who do the work. In this paper, we outline two ways of integrating speciation research: (i) scientific integration, through the bringing together of ideas, data, and approaches; and (ii) social integration, by creating ways for a diversity of researchers to participate in the scientific process. We then discuss five challenges to integration: (i) the multidisciplinary nature of speciation research, (ii) the complex language of speciation; (iii) a bias toward certain study systems; (iv) the challenges of working across scales; and (v) inconsistent measures and reporting standards. We provide practical steps that individuals and groups can take to help overcome these challenges, and argue that integration is a team effort in which we all have a role to play

Toward the integration of speciation research

Acknowledgements: We thank the staff of the Tvärminne Zoological Station (University of Helsinki) for their hospitality during the workshop. We are also grateful to everyone who applied to attend the workshop.Funder: European Society for Evolutionary Biology; DOI: https://doi.org/10.13039/501100013632Speciation research—the scientific field focused on understanding the origin and diversity of species—has a long and complex history. While relevant to one another, the specific goals and activities of speciation researchers are highly diverse, and scattered across a collection of different perspectives. Thus, our understanding of speciation will benefit from efforts to bridge scientific findings and the diverse people who do the work. In this paper, we outline two ways of integrating speciation research: (i) scientific integration, through the bringing together of ideas, data, and approaches; and (ii) social integration, by creating ways for a diversity of researchers to participate in the scientific process. We then discuss five challenges to integration: (i) the multidisciplinary nature of speciation research, (ii) the complex language of speciation; (iii) a bias toward certain study systems; (iv) the challenges of working across scales; and (v) inconsistent measures and reporting standards. We provide practical steps that individuals and groups can take to help overcome these challenges, and argue that integration is a team effort in which we all have a role to play