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In live-bearing animal lineages, the evolution of the placenta is predicted to create an arena for genomic conflict during pregnancy, drive patterns of male sexual selection, and increase the rate of speciation. Here we test these predictions of the viviparity driven conflict hypothesis (VDCH) in live-bearing poecilid fishes, a group showing multiple independent origins of placentation and extreme variation in male sexually selected traits. As predicted, male sexually selected traits are only gained in lineages that lack placentas; while there is little or no influence of male traits on the evolution of placentas. Both results are consistent with the mode of female provisioning governing the evolution of male attributes. Moreover, it is the presence of male sexually selected traits (pre-copulatory), rather than placentation (post-copulatory), that are associated with higher rates of speciation. These results highlight a causal interaction between female reproductive mode, male sexual selection and the rate of speciation, suggesting a role for conflict in shaping diverse aspects of organismal biology.

The evolution of the placenta is an excellent model to examine the evolutionary processes underlying adaptive complexity due to the recent, independent derivation of placentation in divergent animal lineages. In fishes, the family Poeciliidae offers the opportunity to study placental evolution with respect to variation in degree of post-fertilization maternal provisioning among closely related sister species. In this study, we present a detailed examination of a new reference transcriptome sequence for the live-bearing, matrotrophic fish, Poeciliopsis prolifica , from multiple-tissue RNA-seq data. We describe the genetic components active in liver, brain, late-stage embryo, and the maternal placental/ovarian complex, as well as associated patterns of positive selection in a suite of orthologous genes found in fishes. Results indicate the expression of many signaling transcripts, "non-coding" sequences and repetitive elements in the maternal placental/ovarian complex. Moreover, patterns of positive selection in protein sequence evolution were found associated with live-bearing fishes, generally, and the placental P. prolifica , specifically, that appear independent of the general live-bearer lifestyle. Much of the observed patterns of gene expression and positive selection are congruent with the evolution of placentation in fish functionally converging with mammalian placental evolution and with the patterns of rapid evolution facilitated by the teleost-specific whole genome duplication event., (Copyright © 2018 Jue et al.)

Decades of ecological study have demonstrated the importance of top-down and bottom-up controls on food webs, yet few studies within this context have quantified the magnitude of energy and material fluxes at the whole-ecosystem scale. We examined top-down and bottom-up effects on food web fluxes using a field experiment that manipulated the presence of a consumer, the Trinidadian guppy Poecilia reticulata, and the production of basal resources by thinning the riparian forest canopy to increase incident light. To gauge the effects of these reach-scale manipulations on food web fluxes, we used a nitrogen ( 15 N) stable isotope tracer to compare basal resource treatments (thinned canopy vs. control) and consumer treatments (guppy introduction vs. control). The thinned canopy stream had higher primary production than the natural canopy control, leading to increased N fluxes to invertebrates that feed on benthic biofilms (grazers), fine benthic organic matter (collector-gatherers), and organic particles suspended in the water column (filter feeders). Stream reaches with guppies also had higher primary productivity and higher N fluxes to grazers and filter feeders. In contrast, N fluxes to collector-gatherers were reduced in guppy introduction reaches relative to upstream controls. N fluxes to leaf-shredding invertebrates, predatory invertebrates, and the other fish species present (Hart's killifish, Anablepsoides hartii) did not differ across light or guppy treatments, suggesting that effects on detritus-based linkages and upper trophic levels were not as strong. Effect sizes of guppy and canopy treatments on N flux rates were similar for most taxa, though guppy effects were the strongest for filter feeding invertebrates while canopy effects were the strongest for collector-gatherer invertebrates. Combined, these results extend previous knowledge about top-down and bottom-up controls on ecosystems by providing experimental, reach-scale evidence that both pathways can act simultaneously and have equally strong influence on nutrient fluxes from inorganic pools through primary consumers., (© 2016 by the Ecological Society of America.)

Speciation is a multifaceted process that involves numerous aspects of the biological sciences and occurs for multiple reasons. Ecology plays a major role, including both abiotic and biotic factors. Whether populations experience similar or divergent ecological environments, they often adapt to local conditions through divergence in biomechanical traits. We investigate the role of biomechanics in speciation using fish predator-prey interactions, a primary driver of fitness for both predators and prey. We highlight specific groups of fishes, or specific species, that have been particularly valuable for understanding these dynamic interactions and offer the best opportunities for future studies that link genetic architecture to biomechanics and reproductive isolation (RI). In addition to emphasizing the key biomechanical techniques that will be instrumental, we also propose that the movement towards linking biomechanics and speciation will include (i) establishing the genetic basis of biomechanical traits, (ii) testing whether similar and divergent selection lead to biomechanical divergence, and (iii) testing whether/how biomechanical traits affect RI. Future investigations that examine speciation through the lens of biomechanics will propel our understanding of this key process., (© 2016 The Author(s).)

The elemental composition of animals, or their organismal stoichiometry, is thought to constrain their contribution to nutrient recycling, their interactions with other animals, and their demographic rates. Factors that affect organismal stoichiometry are generally poorly understood, but likely reflect elemental investments in morphological features and life history traits, acting in concert with the environmental availability of elements. We assessed the relative contribution of organismal traits and environmental variability to the stoichiometry of an insectivorous Neotropical stream fish, Rivulus hartii. We characterized the influence of body size, life history phenotype, stage of maturity, and environmental variability on organismal stoichiometry in 6 streams that differ in a broad suite of environmental variables. The elemental composition of R. hartii was variable, and overlapped with the wide range of elemental composition documented across freshwater fish taxa. Average %P composition was ∼3.2%(±0.6), average %N∼10.7%(±0.9), and average %C∼41.7%(±3.1). Streams were the strongest predictor of organismal stoichiometry, and explained up to 18% of the overall variance. This effect appeared to be largely explained by variability in quality of basal resources such as epilithon N:P and benthic organic matter C:N, along with variability in invertebrate standing stocks, an important food source for R. hartii. Organismal traits were weak predictors of organismal stoichiometry in this species, explaining when combined up to 7% of the overall variance in stoichiometry. Body size was significantly and positively correlated with %P, and negatively with N:P, and C:P, and life history phenotype was significantly correlated with %C, %P, C:P and C:N. Our study suggests that spatial variability in elemental availability is more strongly correlated with organismal stoichiometry than organismal traits, and suggests that the stoichiometry of carnivores may not be completely buffered from environmental variability. We discuss the relevance of these findings to ecological stoichiometry theory.

Since Smith and Fretwell's seminal article in 1974 on the optimal offspring size, most theory has assumed a trade-off between offspring number and offspring fitness, where larger offspring have better survival or fitness, but with diminishing returns. In this article, we use two ubiquitous biological mechanisms to derive the shape of this trade-off: the offspring's growth rate combined with its size-dependent mortality (predation). For a large parameter region, we obtain the same sigmoid relationship between offspring size and offspring survival as Smith and Fretwell, but we also identify parameter regions where the optimal offspring size is as small or as large as possible. With increasing growth rate, the optimal offspring size is smaller. We then integrate our model with strategies of parental care. Egg guarding that reduces egg mortality favors smaller or larger offspring, depending on how mortality scales with size. For live-bearers, the survival of offspring to birth is a function of maternal survival; if the mother's survival increases with her size, then the model predicts that larger mothers should produce larger offspring. When using parameters for Trinidadian guppies Poecilia reticulata, differences in both growth and size-dependent predation are required to predict observed differences in offspring size between wild populations from high- and low-predation environments.

Changes in age/size-specific mortality, due to such factors as predation, have potent evolutionary consequences. However, interactions with predators commonly impact prey growth rates and food availability and such indirect effects may also influence evolutionary change. We evaluated life-history differences in Trinidadian killifish, Rivulus hartii, across a gradient in predation. Rivulus are located in (1) "high predation" sites with large piscivores, (2) "Rivulus/guppy" sites with guppies, and (3) "Rivulus-only" sites with just Rivulus. Rivulus suffer higher mortality with large predators, and guppies may prey upon small/young Rivulus in Rivulus/guppy environments. In turn, population densities decline while growth rates increase in both localities compared to Rivulus-only sites. To explore how the direct and indirect effects of predators and guppies influence trait diversification in Rivulus, we examined life-history phenotypes across five rivers. High predation phenotypes exhibited a smaller size at reproduction, a greater number of eggs that were smaller, and increased reproductive allotment. Such changes are consistent with a direct response to predation. Rivulus from Rivulus/guppy sites were intermediate; they exhibited a smaller size at reproduction, increased fecundity, smaller eggs, and larger reproductive allotment than Rivulus-only fish. These changes are consistent with models that incorporate the impacts of growth and resources.

Despite abundant examples of both adaptation at the level of phenotype and Darwinian selection at the level of genes, correlations between these two processes are notoriously difficult to identify. Positive Darwinian selection on genes is most easily discerned in cases of genetic conflict, when antagonistic evolutionary processes such as a Red Queen race drive the rate of nonsynonymous substitution above the neutral mutation rate. Genomic imprinting in mammals is thought to be the product of antagonistic evolution coincident with evolution of the placenta, but imprinted loci lack evidence of positive selection likely because of the ancient origin of viviparity in mammals. To determine whether genetic conflict is a general feature of adaptation to placental reproduction, we performed comparative evolutionary analyses of the insulin-like growth factor II (IGF2) gene in teleost fishes. Our analysis included several members of the order Cyprinodontiformes, in which livebearing and placentation have evolved several times independently. We found that IGF2 is subject to positive Darwinian selection coincident with the evolution of placentation in fishes, with particularly strong selection among lineages that have evolved placentation recently. Positive selection is also detected along ancient lineages of placental livebearing fishes, suggesting that selection on IGF2 function is ongoing in placental species. Our observations provide a rare example of natural selection acting in synchrony at the phenotypic and molecular level. These results also constitute the first direct evidence of parent-offspring conflict driving gene evolution.

Classical theories for the evolution of senescence predict that organisms that experience low mortality rates attributable to external factors, such as disease or predation, will evolve a later onset of senescence. Here we use patterns of senescence in guppies derived from natural populations that differ in mortality risk to evaluate the generality of these predictions. We have previously found that populations experiencing higher mortality rates evolve earlier maturity and invest more in reproduction, as predicted by evolutionary theory. We report here that these same populations do not have an earlier onset of senescence with respect to either mortality or reproduction but do with respect to swimming performance, which assesses neuromuscular function. This mosaic pattern of senescence challenges the generality of the association between decreased extrinsic mortality and delayed senescence and invites consideration of more derived theories for the evolution of senescence.

The evolution of the placenta is an excellent model to examine the evolutionary processes underlying adaptive complexity due to the recent, independent derivation of placentation in divergent animal lineages. In fishes, the family Poeciliidae offers the opportunity to study placental evolution with respect to variation in degree of post-fertilization maternal provisioning among closely related sister species. In this study, we present a detailed examination of a new reference transcriptome sequence for the live-bearing, matrotrophic fish, Poeciliopsis prolifica, from multiple-tissue RNA-seq data. We describe the genetic components active in liver, brain, late-stage embryo, and the maternal placental/ovarian complex, as well as associated patterns of positive selection in a suite of orthologous genes found in fishes. Results indicate the expression of many signaling transcripts, "non-coding" sequences and repetitive elements in the maternal placental/ovarian complex. Moreover, patterns of positive selection in protein sequence evolution were found associated with live-bearing fishes, generally, and the placental P. prolifica, specifically, that appear independent of the general live-bearer lifestyle. Much of the observed patterns of gene expression and positive selection are congruent with the evolution of placentation in fish functionally converging with mammalian placental evolution and with the patterns of rapid evolution facilitated by the teleost-specific whole genome duplication event.

Speciation is a multifaceted process that involves numerous aspects of the biological sciences and occurs for multiple reasons. Ecology plays a major role, including both abiotic and biotic factors. Whether populations experience similar or divergent ecological environments, they often adapt to local conditions through divergence in biomechanical traits. We investigate the role of biomechanics in speciation using fish predator-prey interactions, a primary driver of fitness for both predators and prey. We highlight specific groups of fishes, or specific species, that have been particularly valuable for understanding these dynamic interactions and offer the best opportunities for future studies that link genetic architecture to biomechanics and reproductive isolation (RI). In addition to emphasizing the key biomechanical techniques that will be instrumental, we also propose that the movement towards linking biomechanics and speciation will include (i) establishing the genetic basis of biomechanical traits, (ii) testing whether similar and divergent selection lead to biomechanical divergence, and (iii) testing whether/how biomechanical traits affect RI. Future investigations that examine speciation through the lens of biomechanics will propel our understanding of this key process.

Adaptive behavioral plasticity can play a beneficial role when a population becomes established in a novel environment if environmental cues allow the expression of appropriate behavior. Further, plasticity itself can evolve over time in a new environment causing changes in the way or degree to which animals respond to environmental cues. Colonization events provide an opportunity to investigate such relationships between behavioral plasticity and adaptation to new environments. Here, we investigated the evolution of behavior and behavioral plasticity during colonization of a new environment, by testing if female mate‐choice behavior diverged in Trinidadian guppies 2–3 years (~6–9 generations) after being introduced to four locations with reduced predation risk. We collected wild‐caught fish from the source and introduced populations, and we reared out second‐generation females in the laboratory with and without predator cues to examine their plastic responses to a bright and dull male. We found introduced females were less responsive to males when reared without predator cues, but both introduced and source females were similarly responsive when reared with predator cues. Thus, the parallel evolution of behavior across multiple populations in the low‐predation environment was only observed in the treatment mimicking the introduction environment. Such results are consistent with theory predicting that the evolution of plasticity is a by‐product of differential selection across environments. [ABSTRACT FROM AUTHOR]

Maternal effects often provide a mechanism for adaptive transgenerational phenotypic plasticity. The maternal phenotype can profoundly influence the potential for such environmentally induced adjustments of the offspring phenotype, causing correlations between offspring and maternal traits. Here, we study potential effects of the maternal phenotype on offspring provisioning prior to and during gestation in the matrotrophic live‐bearing fish species Poeciliopsis retropinna. Specifically, we examine how maternal traits such as body fat, lean mass, and length relate to pre‐ (i.e., allocation to the egg prior to fertilization) and post‐fertilization (i.e., allocation to the embryo during pregnancy) maternal provisioning and how this ultimately affects offspring size and body composition at birth. We show that pre‐ and post‐fertilization maternal provisioning is associated with maternal length and body fat, but not with maternal lean mass. Maternal length is proportionally associated with egg mass at fertilization and offspring mass at birth, notably without changing the ratio of pre‐ to post‐fertilization maternal provisioning. This ratio, referred to as the matrotrophy index (MI), is often used to quantify the level of matrotrophy. By contrast, the proportion of maternal body fat is positively associated with post‐fertilization, but not pre‐fertilization, maternal provisioning and consequently is strongly positively correlated with the MI. We furthermore found that the composition of embryos changes throughout pregnancy. Females invest first in embryo lean mass, and then allocate fat reserves to embryos very late in pregnancy. We argue that this delay in fat allocation may be adaptive, because it delays an unnecessary high reproductive burden to the mother during earlier stages of pregnancy, potentially leading to a more slender body shape and improved locomotor performance. In conclusion, our study suggests that (a) offspring size at birth is a plastic trait that is predicted by both maternal length and body fat, and (b) the MI is a plastic trait that is predicted solely by the proportion of maternal body fat. It herewith provides new insights into the potential maternal causes and consequences of embryo provisioning during pregnancy in matrotrophic live‐bearing species. Maternal effects are particularly important, frequently having widespread consequences for offspring phenotype and fitness. Here, we studied potential effects of the maternal phenotype on offspring provisioning prior to and during gestation in the matrotrophic live‐bearing fish species Poeciliopsis retropinna. We show that maternal traits strongly correlate with embryo size and body composition throughout pregnancy. Though, different maternal traits are differently related to pre‐ and post‐fertilization maternal provisioning. We furthermore found that the composition of embryos changes during pregnancy independently of the maternal phenotype. [ABSTRACT FROM AUTHOR]

The question of whether populations evolve predictably and consistently under similar selective regimes is fundamental to understanding how adaptation proceeds in the wild. We address this question with a replicated evolution experiment focused upon male sexual coloration in guppies (Poecilia reticulata). Fish were transplanted from a single high predation population in the Guanapo River to four replicate, guppy‐free low predation headwater streams. Two streams had their canopies thinned to adjust the setting under which male coloration is displayed and perceived. We assessed evolutionary divergence using second‐generation lab‐bred offspring of fish sampled four to six years following translocation. A prior experiment of the same design, performed in an adjacent drainage, resulted in the evolution of more extensive orange, black, and iridescent markings. We however found evidence for expansion only in structural coloration (iridescent blue/green), no change in orange, and a reduction in black. This response amplifies earlier findings for Guanapo fish, revealing that trajectories of color elaboration differ among drainages. We also found that color phenotypes evolved more greatly at the thinned‐canopy sites. Our findings support the predictability of sexual trait evolution in the wild, and underscore the importance of signaling conditions and ornamental starting points in shaping adaptive trajectories. [ABSTRACT FROM AUTHOR]

Theory predicts that the sex linkage of sexually selected traits can influence the direction and rate of evolution and should itself evolve in response to sex-specific selection. Some studies have found intraspecific differences in sex linkage associated with differences in selection pressures, but we know nothing about how fast these differences can evolve. Here we show that introduced guppy populations showing rapid evolution of male coloration also show rapid changes in sex-linkage patterns. A comparison, using hormonal manipulations in females, of introduced populations of different ages suggests a consistent increase of autosomal or X-linked coloration 2 years after introduction from high- to low-predation environments. Twenty years after introduction, populations already show the same pattern of coloration inheritance typical of natural low-predation populations in similar habitats. These results highlight that the contemporary evolution of sexually selected traits ought to be studied in concert with contemporary changes in linkage relationships. [ABSTRACT FROM AUTHOR]

Species coexistence may result by chance when co-occurring species do not strongly interact or it may be an evolutionary outcome of strongly interacting species adapting to each other. Although patterns like character displacement indicate that coexistence has often been an evolutionary outcome, it is unclear how often the evolution of coexistence represents adaptation in only one species or reciprocal adaptation among all interacting species. Here, we demonstrate a strong role for evolution in the coexistence of guppies and killifish in Trinidadian streams. We experimentally recreated the temporal stages in the invasion and establishment of guppies into communities that previously contained only killifish. We combined demographic responses of guppies and killifish with a size-based integral projection model to calculate the fitness of the phenotypes of each species in each of the stages of community assembly. We show that guppies from locally adapted populations that are sympatric with killifish have higher fitness when paired with killifish than guppies from allopatric populations. This elevated fitness involves effects traceable to both guppy and killifish evolution. We discuss the implications of our results to the study of species coexistence and how it may be mediated through eco-evolutionary feedbacks. [ABSTRACT FROM AUTHOR]

Raia et al. propose that the evolution of the shape and complexity of animal ornaments (e.g., deer antlers) can be explained by interspecific variation in body size and is not influenced by sexual selection. They claim to show that ornament complexity is related to body size by an 0.25-power law and argue that this finding precludes a role for sexual selection in the evolution of ornament complexity. However, their study does not test alternative hypotheses and mismeasures antler shape allometry by omitting much of the published data. We show that an index of sexual selection (sexual size dimorphism) is positively correlated with size-corrected antler complexity and that the allometric slope of complexity is substantially greater than 0.25, contra Raia et al. We conclude that sexual selection and physical constraints both affect the evolution of antler shape. [ABSTRACT FROM AUTHOR]

Genetic rescue, an increase in population growth owing to the infusion of new alleles, can aid the persistence of small populations. Its use as a management tool is limited by a lack of empirical data geared toward predicting effects of gene flow on local adaptation and demography. Experimental translocations provide an ideal opportunity to monitor the demographic consequences of gene flow. In this study we take advantage of two experimental introductions of Trinidadian guppies to test the effects of gene flow on downstream native populations. We individually marked guppies from the native populations to monitor population dynamics for 3 months before and 26 months after gene flow. We genotyped all individuals caught during the first 17 months at microsatellite loci to classify individuals by their genetic ancestry: native, immigrant, F1 hybrid, F2 hybrid, or backcross. Our study documents a combination of demographic and genetic rescue over multiple generations under fully natural conditions. Within both recipient populations, we found substantial and long-term increases in population size that could be attributed to high survival and recruitment caused by immigration and gene flow from the introduction sites. Our results suggest that low levels of gene flow, even from a divergent ecotype, can provide a substantial demographic boost to small populations, which may allow them to withstand environmental stochasticity. [ABSTRACT FROM AUTHOR]

Phenotypic plasticity is advantageous for organisms that live in variable environments. The digestive system is particularly plastic, responding to changes in diet. Gut length is the result of a trade-off between maximum nutrient absorption and minimum cost for its maintenance and it can be influenced by diet and by evolutionary history. We assessed variation in gut length of Trinidadian guppies (Poecilia reticulata) as a function of diet, season, ontogeny, and local adaptation. Populations of guppies adapted to different predation levels have evolved different life history traits and have different diets. We sampled guppies from sites with low (LP) and high predation (HP) pressure in the Aripo and Guanapo Rivers in Trinidad. We collected fish during both the dry and wet season and assessed their diet and gut length. During the dry season, guppies from HP sites fed mostly on invertebrates, while guppies in the LP sites fed mainly on detritus. During the wet season, the diet of LP and HP populations became very similar. We did not find strong evidence of an ontogenetic diet shift. Gut length was negatively correlated with the proportion of invertebrates in diet across fish from all sites, supporting the hypothesis that guppy digestive systems adapt in length to changes in diet. Population of origin also had an effect on gut length, as HP and LP fish maintained different gut lengths even in the wet season, when their diets were very similar and individuals in both types of populations fed mostly on detritus. Thus, both environment and population of origin influenced guppies gut length, but population of origin seemed to have a stronger effect. Our study also showed that, even in omnivorous fish, gut length adapted to different diets, being more evident when the magnitude of difference between animal and plant material in the diet was very large. [ABSTRACT FROM AUTHOR]

Two ways in which organisms adapt to variable environments are phenotypic plasticity and bet-hedging. Theory suggests that bet-hedging is expected to evolve in unpredictable environments for which reliable cues indicative of future conditions (or season length) are lacking. Alternatively, if reliable cues exist indicating future conditions, organisms will be under selection to produce the most appropriate phenotype -that is, adaptive phenotypic plasticity. Here, we experimentally test which of these modes of adaptation are at play in killifish that have evolved an annual life cycle. These fish persist in ephemeral pools that completely dry each season through the production of eggs that can remain in developmental arrest, or diapause, buried in the soil, until the following rainy season. Consistent with diversified bet-hedging (a risk spreading strategy), we demonstrate that the eggs of the annual killifish Nothobranchius furzeri exhibit variation at multiple levels-whether or not different stages of diapause are entered, for how long diapause is entered, and the timing of hatching-and this variation persists after controlling for both genetic and environmental sources of variation. However, we show that phenotypic plasticity is also present in that the proportion of eggs that enter diapause is influenced by environmental factors (temperature and light level) that vary seasonally. In nature there is typically a large parameter zone where environmental cues are somewhat correlated with seasonality, but not perfectly so, such that it may be advantageous to have a combination of both bet-hedging and plasticity. [ABSTRACT FROM AUTHOR]

Sexual selection can increase morphological diversity within and among species. Little is known regarding how interspecific variation produced through sexual selection affects other functional systems. Here, we examine how morphological diversity resulting from sexual selection impacts aerobic locomotor performance. Using Xiphophorus (swordtail fish) and their close relatives ( N = 19 species), we examined whether the evolution of a longer sexually selected sword affects critical swimming speed. We also examined the effect of other suborganismal, physiological, and morphological traits on critical swimming speed, as well as their relationship with sword length. In correlation analyses, we found no significant relationship between sword length and critical swimming speed. Unexpectedly, we found that critical swimming speed was higher in species with longer swords, after controlling for body size in multiple regression analyses. We also found several suborganismal and morphological predictors of critical swimming speed, as well as a significant negative relationship between sword length and heart and gill mass. Our results suggest that interspecific variation in sword length is not costly for this aspect of swimming performance, but further studies should examine potential costs for other types of locomotion and other components of Darwinian fitness (e.g., survivorship, life span). [ABSTRACT FROM AUTHOR]

1. Environmental conditions in the present, more recent past and during the juvenile stage can have significant effects on adult performance and population dynamics, but their relative importance and potential interactions remain unexplored. 2. We examined the influence of food availability at the time of sampling, 2 months prior and during the juvenile stage on adult somatic growth rates in wild Trinidadian guppies ( Poecilia reticulata). 3. We found that food availability during both the early and later parts of an individual's ontogeny had important consequences for adult growth strategies, but the direction of these effects differed among life stages and their magnitude, in some cases, depended on food levels experienced during other life stages. Current food levels and those 2 months prior to growth measurements had positive effects on adult growth rate; though, food levels 2 months prior had a greater effect on growth than current food levels. In contrast, the effects of food availability during the juvenile stage were higher in magnitude but opposite in direction to current food levels and those 2 months prior to growth rate measurements. Individuals recruiting under low food levels grew faster as adults than individuals recruiting during periods of high food availability. There was also a positive interaction between food levels experienced during the juvenile stage and 2 months prior such that the effects of juvenile food level diminished as the food level experienced 2 months prior increased. 4. These results suggest that the similar conditions occurring at different life stages can have different effects on short- and long-term growth strategies of individuals within a population. They also demonstrate that, while juvenile conditions can have lasting effects on adult performance, the strength of that effect can be dampened by environmental conditions experienced as an adult. 5. A simultaneous consideration of past events in both the adult and juvenile stage may therefore improve predictions for individual- and population-level responses to environmental change. [ABSTRACT FROM AUTHOR]

Evolutionary theory predicts that the sex linkage of sexually selected traits can influence the direction and rate of evolutionary change, and also itself be subject to selection. Theory abounds on how sex-specific selection, mate choice, or other phenomena should favor different types of sex-linked inheritance, yet evidence in nature remains limited. Here, we use hormone assays in Trinidadian guppies to explore the extent to which linkage of male coloration differs among populations adapted to varying predation regimes. Results show there is consistently higher degree of X- and autosomal linkage in body coloration among populations adapted to low-predation environments. More strikingly, analyses of an introduced population of guppies from a high- to a low-predation environment suggest that this difference can change in 50 years or less. [ABSTRACT FROM AUTHOR]

Matrotrophic fish in the genus Poeciliopsis (Poeciliidae) have a placenta-like structure used in postfertilization maternal provisioning of the developing embryo. To understand better the structure and function of the Poeciliopsis placenta, we derived cDNA libraries from the maternal follicular placenta of 2 matrotrophic Poeciliopsis sister species, P. turneri and P. presidionis. These species inherited their placenta from a common ancestor and represent one of 3 independent origins of placentas in Poeciliopsis. Expressed sequence tags (ESTs) were generated and putative function was determined using BLASTX homology searches and Gene Ontology (GO) annotation. Reverse transcription–polymerase chain reaction was used to verify placenta tissue expression of a putative candidate gene, alpha-2 macroglobulin. In total, 1956 (71.5% of the total submitted ESTs) and 924 (71.0% of the total submitted ESTs) unique transcripts were identified for the P. turneri and P. presidionis placenta, respectively. Homology search and GO annotation revealed putative genes whose products may be involved in specific transport functions of the maternal follicle. These putative genes are excellent candidates for future research on the evolution of the placenta. We discuss our results in light of the parent–offspring conflict theory of placental evolution and in terms of the Poeciliid placenta structure and function. [ABSTRACT FROM PUBLISHER]

Complex adaptations are often found in nature, although our ability to discern how and why such traits evolved is limited because their origin occurred in the distant past and the details of their evolution have been lost through extinction (e.g. all placental mammals inherited their placentas from a single common ancestor that lived over 100 Mya). In poeciliid fishes, placentas have evolved independently multiple times and portions of the path to the evolution of complexity can be found in living species. In the present study, we describe the life histories of six species within the genus Poecilia that includes the subgenera Micropoecilia and Acanthophacelus (the guppy; Poecilia reticulata). We demonstrate that extensive placentotrophy and superfetation, the ability to simultaneously carry more than one developing brood, have evolved within this clade. These fish represent the third clade in which we have discovered the independent origin of a placenta that also includes close relatives that lack a placenta. We discuss possible adaptive advantages of the joint evolution of extensive placentation and superfetation in these fishes. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 99, 784–796. [ABSTRACT FROM AUTHOR]