The evolution of coloniality: the emergence of new perspectives

The evolution of group living remains an outstanding question in evolutionary ecology. Among the most striking forms of group living are the enormous assemblages of breeders that occur in many colonial marine birds and mammals, with some colonies containing more than a million individuals breeding in close contact. Coloniality is an evolutionary puzzle because individuals pay fitness costs to breed in high densities. Despite numerous potential benefits proposed to overcome these costs, we still lack a general framework to explain coloniality. Several new hypotheses involving breeding habitat and mate selection create promising approaches for studying this enigma.     

A multi-gene phylogeny of Cephalopoda supports convergent morphological evolution in association with multiple habitat shifts in the marine environment

ABSTRACT: BACKGROUND: The marine environment is comprised of numerous divergent organisms living under similar selective pressures, often resulting in the evolution of convergent structures such as the fusiform body shape of pelagic squids, fishes, and some marine mammals. However, little is known about the frequency of, and circumstances leading to, convergent evolution in the open ocean. Here, we present a comparative study of the molluscan class Cephalopoda, a marine group known to occupy habitats from the intertidal to the deep sea. Several lineages bear features that may coincide with a benthic or pelagic existence, making this a valuable group for testing hypotheses of correlated evolution. To test for convergence and correlation, we generate the most taxonomically comprehensive multi-gene phylogeny of cephalopods to date. We then create a character matrix of habitat type and morphological characters, which we use to infer ancestral character states and test for correlation between habitat and morphology. RESULTS: Our study utilizes a taxonomically well-sampled phylogeny to show convergent evolution in all six morphological characters we analyzed. Three of these characters also correlate with habitat. The presence of an autogenic photophore is correlated with a pelagic habitat, while the cornea and accessory nidamental gland correlate with a benthic lifestyle. Here, we present the first statistical tests for correlation between convergent traits and habitat in cephalopods to better understand the evolutionary history of characters that are adaptive in benthic or pelagic environments, respectively. DISCUSSION: Our study supports the hypothesis that habitat has influenced convergent evolution in the marine environment: benthic organisms tend to exhibit similar characteristics that confer protection from invasion by other benthic taxa, while pelagic organisms possess features that facilitate crypsis and communication in an environment lacking physical refuges. Features that have originated multiple times in distantly related lineages are likely adaptive for the organisms inhabiting a particular environment: studying the frequency and evolutionary history of such convergent characters can increase understanding of the underlying forces driving ecological and evolutionary transitions in the marine environment.     

Mate fidelity and coloniality in waterbirds: a comparative analysis

Increased opportunities for information are one potential benefit of sociality. We apply this idea to the advantages of colonial breeding in bird species that are typically monogamous within a breeding season but often form new pair-bonds in subsequent seasons. Individuals may benefit from nesting in colonies at high density by identifying good-quality potential alternative mates among their neighbours. The opportunities for finding a better mating option are likely to increase with colony size and density. We tested this prediction with a comparative analysis of the association between mate fidelity and coloniality in waterbirds (wading birds and seabirds), where there is wide variation in both the degree of mate retention over consecutive breeding seasons and the degree of coloniality. We used two comparative statistical analyses, one based upon generalized least squares and the other based upon a continuous-time Markov model, to test whether the pattern of association between divorce rate and degree of coloniality was evidence for correlated evolutionary change in the two characters. We found a significant and positive association between divorce rate and the degree of coloniality in waterbirds. The probable ancestral state corresponds to a combination of a high degree of coloniality with no, or weak, mate fidelity. The reconstruction of the historical pattern of character origin and evolution indicates that the transition from a high to a low degree of coloniality occurred before the transition to higher mate fidelity. Received: 5 January 1998 / Accepted: 20 April 1998     

Marine lifestyle is associated with higher baseline corticosterone levels in birds

Because seawater is hyperosmotic relative to body fluids of most vertebrates, marine lifestyle is expected to strongly influence the physiology of marine tetrapods. Regulating the salt content of body fluids is energetically costly; and osmoregulatory organs may not totally overcome salt load and/or water loss. As a consequence, marine lifestyle should influence physiological systems involved in the maintenance of the physiological balance (homeostasis), in the mobilisation of energetic resources (e.g., to fuel salt excretion), or in the acquisition of resources (e.g., fresh water). Corticosterone (CORT) is one such ‘generalist’ mediator that is linked with energy expenditure, physiological stress and that activates osmoregulation. As a consequence, CORT is expected to be overall higher in marine tetrapods but this hypothesis has never been tested. Using comparative analyses, we tested this hypothesis in birds, a lineage for which available data on baseline CORT allow comparing marine versus terrestrial species, and species with or without salt glands. We found that marine species (and species with salt glands) display significantly higher baseline CORT during the wintering (but not the breeding) stage. Although salt glands’ presence was tightly linked to phylogeny, our results suggest that marine lifestyle may impose a strong, but overlooked, influence on the allostasis‐related physiology of marine birds. Such habitat‐related variation in physiology is a major phenomenon to explore owing to its general implications for understanding the physiological basis of evolutionary transitions in habitat use. © 2015 The Linnean Society of London, Biological Journal of the Linnean Society, 2015, 115 , 154–161.     

Widespread and persistent invasions of terrestrial habitats coincident with larval feeding behavior transitions during snail-killing fly evolution (Diptera: Sciomyzidae)

ABSTRACT: BACKGROUND: Transitions in habitats and feeding behaviors were fundamental to the diversification of life on Earth. There is ongoing debate regarding the typical directionality of transitions between aquatic and terrestrial habitats and the mechanisms responsible for the preponderance of terrestrial to aquatic transitions. Snail-killing flies (Diptera: Sciomyzidae) represent an excellent model system to study such transitions because their larvae display a range of feeding behaviors, being predators, parasitoids or saprophages of a variety of mollusks in freshwater, shoreline and dry terrestrial habitats. The remarkable genus Tetanocera (Tetanocerini) occupies five larval feeding groups and all of the habitat types mentioned above. This study has four principal objectives: (i) construct a robust estimate of phylogeny for Tetanocera and Tetanocerini, (ii) estimate the evolutionary transitions in larval feeding behaviors and habitats, (iii) test the monophyly of feeding groups and (iv) identify mechanisms underlying sciomyzid habitat and feeding behavior evolution. RESULTS: Bayesian inference and maximum likelihood analyses of molecular data provided strong support that the Sciomyzini, Tetanocerini and Tetanocera are monophyletic. However, the monophyly of many behavioral groupings was rejected via phylogenetic constraint analyses. We determined that (i) the ancestral sciomyzid lineage was terrestrial, (ii) there was a single terrestrial to aquatic habitat transition early in the evolution of the Tetanocerini and (iii) there were at least 10 independent aquatic to terrestrial habitat transitions and at least 15 feeding behavior transitions during tetanocerine phylogenesis. The ancestor of Tetanocera was aquatic with five lineages making independent transitions to terrestrial habitats and seven making independent transitions in feeding behaviors. CONCLUSIONS: The preponderance of aquatic to terrestrial transitions in sciomyzids goes against the trend generally observed across eukaryotes. Damp shoreline habitats are likely transitional where larvae can change habitat but still have similar prey available. Transitioning from aquatic to terrestrial habitats is likely easier than the reverse for sciomyzids because morphological characters associated with air-breathing while under the water's surface are lost rather than gained, and sciomyzids originated and diversified during a general drying period in Earth's history. Our results imply that any animal lineage having aquatic and terrestrial members, respiring the same way in both habitats and having the same type of food available in both habitats could show a similar pattern of multiple independent habitat transitions coincident with changes in behavioral and morphological traits.     

Correlated Evolution between Mode of Larval Development and Habitat in Muricid Gastropods

Larval modes of development affect evolutionary processes and influence the distribution of marine invertebrates in the ocean. The decrease in pelagic development toward higher latitudes is one of the patterns of distribution most frequently discussed in marine organisms (Thorson''s rule), which has been related to increased larval mortality associated with long pelagic durations in colder waters. However, the type of substrate occupied by adults has been suggested to influence the generality of the latitudinal patterns in larval development. To help understand how the environment affects the evolution of larval types we evaluated the association between larval development and habitat using gastropods of the Muricidae family as a model group. To achieve this goal, we collected information on latitudinal distribution, sea water temperature, larval development and type of substrate occupied by adults. We constructed a molecular phylogeny for 45 species of muricids to estimate the ancestral character states and to assess the relationship between traits using comparative methods in a Bayesian framework. Our results showed high probability for a common ancestor of the muricids with nonpelagic (and nonfeeding) development, that lived in hard bottoms and cold temperatures. From this ancestor, a pelagic feeding larva evolved three times, and some species shifted to warmer temperatures or sand bottoms. The evolution of larval development was not independent of habitat; the most probable evolutionary route reconstructed in the analysis of correlated evolution showed that type of larval development may change in soft bottoms but in hard bottoms this change is highly unlikely. Lower sea water temperatures were associated with nonpelagic modes of development, supporting Thorson''s rule. We show how environmental pressures can favor a particular mode of larval development or transitions between larval modes and discuss the reacquisition of feeding larva in muricids gastropods.     

Distinct evolutionary patterns of morphometric sperm traits in passerine birds

The striking diversity of sperm shape across the animal kingdom is still poorly understood. Postcopulatory sexual selection is an important factor driving the evolution of sperm size and shape. Interestingly, morphometric sperm traits, such as the length of the head, midpiece and flagellum, exhibit a strong positive phenotypic correlation across species. Here we used recently developed comparative methods to investigate how such phenotypic correlations between morphometric sperm traits may evolve. We compare allometric relationships and evolutionary trajectories of three morphometric sperm traits (length of head, midpiece and flagellum) in passerine birds. We show that these traits exhibit strong phenotypic correlations but that allometry varies across families. In addition, the evolutionary trajectories of the midpiece and flagellum are similar while the trajectory for head length differs. We discuss our findings in the light of three scenarios accounting for correlated trait evolution: (i) genetic correlation; (ii) concerted response to selection acting simultaneously on different traits; and (iii) phenotypic correlation between traits driven by mechanistic constraints owing to selection on sperm performance. Our results suggest that concerted response to selection is the most likely explanation for the phenotypic correlation between morphometric sperm traits.     

The evolution of larval morphology and swimming performance in ascidians

The complexity of organismal function challenges our ability to understand the evolution of animal locomotion. To meet this challenge, we used a combination of biomechanics, phylogenetic comparative analyses, and theoretical morphology to examine evolutionary changes in body shape and how those changes affected swimming performance in ascidian larvae. Results of phylogenetic comparative analyses suggest that coloniality evolved at least three times among ascidians and that colonial species have a convergent larval morphology characterized by a large trunk volume and shorter tail length in proportion to the trunk. To explore the functional significance of this evolutionary change, we first verified the accuracy of a mathematical model of swimming biomechanics in a solitary (C. intestinalis) and a colonial (D. occidentalis) species and then ran numerous simulations of the model that varied in tail length and trunk volume. The results of these simulations were used to construct landscapes of speed and cost of transport predictions within a trunk volume/tail length morphospace. Our results suggest that the reduction of proportionate tail length in colonial species resulted in improved energetic economy of swimming. The increase in the size of larvae with the origin of coloniality facilitated faster swimming with negligible energetic cost, but may have required a reduction in adult fecundity. Therefore, the evolution of ascidians appears to be influenced by a trade-off between the fecundity of the adult stage and the swimming performance of larvae.     

The evolution of habitat specialisation in a group of marine triplefin fishes

There has been considerable interest in the directionality of resource specialisation during the diversification of lineages. We developed a quantitative method to investigate habitat specialisation in a radiation of New Zealand triplefin fishes, as habitat use appears to be an important axis of diversification in this marine group. The degree of specialisation in 15 species was calculated by comparing each individual to all other individuals of a species, thus allowing for quantitative distinction between species. Species differed in habitat specialisation, but Bayesian comparative methods found no directional trend in the evolution of resource use. Further analyses showed that specialisation had evolved gradually and was phylogenetically constrained, with most differences between species arising toward the tips of the tree. No correlation between the degree of specialisation and body size was detected in this group, suggesting that habitat specialisation evolved independently of body size. Habitat specialisation does not appear to have been an impediment to ecological diversification in this group. Rather, diversification in these fishes appears to have followed different evolutionary trajectories in habitat specialisation, one in which species have sub-partitioned available resources, and another in which species have expanded their use of resources. These findings support recent studies suggesting that diversification does not necessarily proceed from generalised ancestors to specialised descendants.     

Correlated evolution and Bayesian divergence time estimates of the Cimicoidea (Heteroptera: Cimicomorpha) reveal the evolutionary history

The diverse habitat types and discrete morphological characters of cimicoid species provide a unique opportunity to study correlated evolution. Phylogenetic relationships within Cimicoidea were determined using Bayesian analyses of molecular data, allowing the generation of testable hypotheses of correlated evolution. An investigation of the correlation between habitat selection and morphological characters revealed that a dead plant habitat was correlated with the filiform antennal type. Furthermore, molecular dating analysis was used to examine divergence times within the Cimicoidea. Transitions to live plants from dead plants for most cimicoid clades started right after the mid‐Cretaceous, coinciding with the radiation of the angiosperms. Using contingency analyses, we determined that evolutionary changes in morphological characters were dependent on habitat selection. Based on these results, we propose evolutionary historical hypotheses for the Cimicoidea.     

The Evolution of Olfactory Capabilities in Wild Birds: A Comparative Study

Modern birds possess an olfactory apparatus similar to that of other vertebrates, yet the major evolutionary forces that drove the evolution of diversity in olfactory capabilities in birds remain elusive. Several non-mutually exclusive evolutionary scenarios for the evolution of olfactory capability in birds have been proposed. Olfactory capability may have evolved due to its role in recognition in social contexts. In addition, olfactory capability may have evolved because it provides a selective advantage in foraging or navigation. Finally, olfactory capability could be favored whenever the ecological conditions of species hindered the use of other senses and/or favored olfaction. Here we evaluate predictions from these hypotheses in a comparative study using a species-level phylogeny of 142 bird species and considering the indirect effects of some predictors on others. We find an interactive effect of aquatic dependence and diet on the size of the olfactory bulb: vegetarian and omnivore birds living in aquatic environments have larger olfactory bulbs than terrestrial birds, whereas species with an animal diet, aquatic and terrestrial species have similar-sized olfactory bulbs. In addition, the size of the olfactory bulb was weakly related with social complexity, with colonial species having relatively larger olfactory bulb than solitary breeders or those forming small aggregations. Our results suggest that the role of foraging in driving enhancements in the avian olfactory apparatus is contingent on ecological conditions that may affect the transmission of odor-based signals. This provides evidence for the largely neglected possibility that the evolution of the olfactory apparatus of birds has been driven by the interaction between ecological and behavioral traits, rather than being solely due to main effects of these traits.     

Determinants of local abundance in a major radiation of Australian passerines (Aves: Meliphagoidea)

Aim  To identify the factors that contribute to variation in abundance (population density), and to investigate whether habitat breadth and diet breadth predict macroecological patterns in a suborder of passerine birds (Meliphagoidea).
Location  Australia (including Tasmania).
Methods  Mean abundance data were collated from site surveys of bird abundance (the Australian Bird Count); range size and latitudinal position data from published distribution maps; and body mass and diet breadth information from published accounts. A diversity index of habitats used (habitat breadth) was calculated from the bird census data. We used bivariate correlation and multiple regression techniques, employing two phylogenetic comparative methods: phylogenetic generalized least squares and independent contrasts.
Results  Body mass and latitude were the only strong predictors of abundance, with larger-bodied and lower-latitude species existing at lower densities. Together, however, body mass and latitude explained only 11.1% of the variation in mean abundance. Range size and habitat breadth were positively correlated, as were diet breadth and body mass. However, neither range size, nor habitat breadth and diet breadth, explained patterns in abundance either directly or indirectly.
Main conclusions  Levels of abundance (population density) in meliphagoid birds are most closely linked to body mass and latitudinal position, but not range size. As with many other macroecological analyses, we find little evidence for aspects of niche breadth having an effect on patterns of abundance. We hypothesize that evolutionary age may also have a determining effect on why species tend to be rarer (less abundant) in the tropics.     

The first chromosome‐level genome for a marine mammal as a resource to study ecology and evolution

Marine mammals are important models for studying convergent evolution and aquatic adaption, and thus reference genomes of marine mammals can provide evolutionary insights. Here, we present the first chromosome‐level marine mammal genome assembly based on the data generated by the BGISEQ‐500 platform, for a stranded female sperm whale (Physeter macrocephalus). Using this reference genome, we performed chromosome evolution analysis of the sperm whale, including constructing ancestral chromosomes, identifying chromosome rearrangement events and comparing with cattle chromosomes, which provides a resource for exploring marine mammal adaptation and speciation. We detected a high proportion of long interspersed nuclear elements and expanded gene families, and contraction of major histocompatibility complex region genes which were specific to sperm whale. Using comparisons with sheep and cattle, we analysed positively selected genes to identify gene pathways that may be related to adaptation to the marine environment. Further, we identified possible convergent evolution in aquatic mammals by testing for positively selected genes across three orders of marine mammals. In addition, we used publicly available resequencing data to confirm a rapid decline in global population size in the Pliocene to Pleistocene transition. This study sheds light on the chromosome evolution and genetic mechanisms underpinning sperm whale adaptations, providing valuable resources for future comparative genomics.     

Evolution of sexual systems, dispersal strategies and habitat selection in the liverwort genus Radula

? Shifts in sexual systems are among the most common and important transitions in plants and are correlated with a suite of life-history traits. The evolution of sexual systems and their relationships to gametophyte size, sexual and asexual reproduction, and epiphytism are examined here in the liverwort genus Radula. ? The sequence of trait acquisition and the phylogenetic correlations between those traits was investigated using comparative methods. ? Shifts in sexual systems recurrently occurred from dioecy to monoecy within facultative epiphyte lineages. Production of specialized asexual gemmae was correlated to neither dioecy nor strict epiphytism. ? The significant correlations among life-history traits related to sexual systems and habitat conditions suggest the existence of evolutionary trade-offs. Obligate epiphytes do not produce gemmae more frequently than facultative epiphytes and disperse by whole gametophyte fragments, presumably to avoid the sensitive protonemal stage in a habitat prone to rapid changes in moisture availability. As dispersal ranges correlate with diaspore size, this reinforces the notion that epiphytes experience strong dispersal limitations. Our results thus provide the evolutionary complement to metapopulation, metacommunity and experimental studies demonstrating trade-offs between dispersal distance, establishment ability, and life-history strategy, which may be central to the evolution of reproductive strategies in bryophytes.     

ELEVATED RATES OF MORPHOLOGICAL AND FUNCTIONAL DIVERSIFICATION IN REEF‐DWELLING HAEMULID FISHES

The relationship between habitat complexity and species richness is well established but comparatively little is known about the evolution of morphological diversity in complex habitats. Reefs are structurally complex, highly productive shallow‐water marine ecosystems found in tropical (coral reefs) and temperate zones (rocky reefs) that harbor exceptional levels of biodiversity. We investigated whether reef habitats promote the evolution of morphological diversity in the feeding and locomotion systems of grunts (Haemulidae), a group of predominantly nocturnal fishes that live on both temperate and tropical reefs. Using phylogenetic comparative methods and statistical analyses that take into account uncertainty in phylogeny and the evolutionary history of reef living, we demonstrate that rates of morphological evolution are faster in reef‐dwelling haemulids. The magnitude of this effect depends on the type of trait; on average, traits involved in the functional systems for prey capture and processing evolve twice as fast on reefs as locomotor traits. This result, along with the observation that haemulids do not exploit unique feeding niches on reefs, suggests that fine‐scale trophic niche partitioning and character displacement may be driving higher rates of morphological evolution. Whatever the cause, there is growing evidence that reef habitats stimulate morphological and functional diversification in teleost fishes.     

Coevolving avian eye size and brain size in relation to prey capture and nocturnality

Behavioural adaptation to ecological conditions can lead to brain size evolution. Structures involved in behavioural visual information processing are expected to coevolve with enlargement of the brain. Because birds are mainly vision-oriented animals, we tested the predictions that adaptation to different foraging constraints can result in eye size evolution, and that species with large eyes have evolved large brains to cope with the increased amount of visual input. Using a comparative approach, we investigated the relationship between eye size and brain size, and the effect of prey capture technique and nocturnality on these traits. After controlling for allometric effects, there was a significant, positive correlation between relative brain size and relative eye size. Variation in relative eye and brain size were significantly and positively related to prey capture technique and nocturnality when a potentially confounding variable, aquatic feeding, was controlled statistically in multiple regression of independent linear contrasts. Applying a less robust, brunching approach, these patterns also emerged, with the exception that relative brain size did not vary with prey capture technique. Our findings suggest that relative eye size and brain size have coevolved in birds in response to nocturnal activity and, at least partly, to capture of mobile prey.     

Lake Malawi cichlid evolution along a benthic/limnetic axis

Divergence along a benthic to limnetic habitat axis is ubiquitous in aquatic systems. However, this type of habitat divergence has largely been examined in low diversity, high latitude lake systems. In this study, we examined the importance of benthic and limnetic divergence within the incredibly species‐rich radiation of Lake Malawi cichlid fishes. Using novel phylogenetic reconstructions, we provided a series of hypotheses regarding the evolutionary relationships among 24 benthic and limnetic species that suggests divergence along this axis has occurred multiple times within Lake Malawi cichlids. Because pectoral fin morphology is often associated with divergence along this habitat axis in other fish groups, we investigated divergence in pectoral fin muscles in these benthic and limnetic cichlid species. We showed that the eight pectoral fin muscles and fin area generally tended to evolve in a tightly correlated manner in the Lake Malawi cichlids. Additionally, we found that larger pectoral fin muscles are strongly associated with the independent evolution of the benthic feeding habit across this group of fish. Evolutionary specialization along a benthic/limnetic axis has occurred multiple times within this tropical lake radiation and has produced repeated convergent matching between exploitation of water column habitats and locomotory morphology.     

Does predation select for or against avian coloniality? A comparative analysis

Some studies have supported predation as a selective pressure contributing to the evolution of coloniality. However, evidence also exists that colonies attract predators, selecting against colonial breeding. Using comparative analyses, we tested the reduced predation hypothesis that individuals aggregate into colonies for protection, and the opposite hypothesis, that breeding aggregations increase predation risk. We used locational and physical characteristics of nests to estimate levels of species' vulnerability to predation. We analysed the Ciconiiformes, a large avian order with the highest prevalence of coloniality, using Pagel's general method of comparative analysis for discrete variables. A common requirement of both hypotheses, that there is correlated evolution between coloniality and vulnerability to predation, was fulfilled in our data set of 363 species. The main predictions of the reduced predation hypothesis were not supported, namely that (1) solitary/vulnerable species are more prone to become colonial than solitary/protected species and (2) colonial/protected species are more likely to evolve towards vulnerability than solitary/protected species. In contrast, the main predictions of the increased predation hypothesis were supported, namely that colonial/vulnerable species are more prone (1) to become protected than solitary/vulnerable species and/or (2) to become solitary than colonial/protected species. This suggests that the colonial/vulnerable state is especially exposed to predation as coloniality may often attract predators rather than provide safety.     

Comparative genomics reveals insights into cyanobacterial evolution and habitat adaptation

Cyanobacteria are photosynthetic prokaryotes that inhabit diverse aquatic and terrestrial environments. However, the evolutionary mechanisms involved in the cyanobacterial habitat adaptation remain poorly understood. Here, based on phylogenetic and comparative genomic analyses of 650 cyanobacterial genomes, we investigated the genetic basis of cyanobacterial habitat adaptation (marine, freshwater, and terrestrial). We show: (1) the expansion of gene families is a common strategy whereby terrestrial cyanobacteria cope with fluctuating environments, whereas the genomes of many marine strains have undergone contraction to adapt to nutrient-poor conditions. (2) Hundreds of genes are strongly associated with specific habitats. Genes that are differentially abundant in genomes of marine, freshwater, and terrestrial cyanobacteria were found to be involved in light sensing and absorption, chemotaxis, nutrient transporters, responses to osmotic stress, etc., indicating the importance of these genes in the survival and adaptation of organisms in specific habitats. (3) A substantial fraction of genes that facilitate the adaptation of Cyanobacteria to specific habitats are contributed by horizontal gene transfer, and such genetic exchanges are more frequent in terrestrial cyanobacteria. Collectively, our results further our understandings of the adaptations of Cyanobacteria to different environments, highlighting the importance of ecological constraints imposed by the environment in shaping the evolution of Cyanobacteria.Subject terms: Phylogenetics, Microbial ecology     

The evolution of dispersal in reserve networks

The fragmentation of an environment into developed and protected areas may influence selection pressure on dispersal by increasing the chance of moving from a favorable to an unfavorable habitat. We theoretically explore this possibility through two cases: (1) marine systems in which reduced predation and/or increased feeding drive the evolution of planktonic larval duration and (2) more generally, where stochasticity in reproductive yield drives the evolution of the proportion of offspring dispersing. Model results indicate that habitat fragmentation generally shifts selection pressure toward reduced dispersal, particularly when areas outside reserves are uninhabitable. However, shifts to increased dispersal may occur when temporal heterogeneity is the primary selective force and constant-quota harvest occurs outside reserves. In addition, model results suggest the potential for changes in the genetic variability in dispersal after habitat fragmentation. The predicted evolutionary changes in dispersal will depend on factors such as the relative genetic and environmental contributions to dispersal-related traits and the extent of anthropogenic impacts outside reserves. If the predicted evolutionary changes are biologically attainable, they may suggest altering current guidelines for the appropriate size and spacing of marine reserves necessary to achieve conservation and fisheries goals.