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Morphological divergence driven by predation environment within and between species of Brachyrhaphis fishes.

Ingley SJ, Billman EJ, Belk MC, Johnson JB - PLoS ONE (2014)

Bottom Line: Natural selection often results in profound differences in body shape among populations from divergent selective environments.Interestingly, at both levels of divergence we found that early in ontogenetic development, females differed in shape between predation environments; however, as females matured, their body shapes converged on a similar phenotype, likely due to the constraints of pregnancy.Finally, we found that body shape varies with body size in a similar way, regardless of predation environment, in each lineage.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, Brigham Young University, Provo, Utah, United States of America.

ABSTRACT
Natural selection often results in profound differences in body shape among populations from divergent selective environments. Predation is a well-studied driver of divergence, with predators having a strong effect on the evolution of prey body shape, especially for traits related to escape behavior. Comparative studies, both at the population level and between species, show that the presence or absence of predators can alter prey morphology. Although this pattern is well documented in various species or population pairs, few studies have tested for similar patterns of body shape evolution at multiple stages of divergence within a taxonomic group. Here, we examine morphological divergence associated with predation environment in the livebearing fish genus Brachyrhaphis. We compare differences in body shape between populations of B. rhabdophora from different predation environments to differences in body shape between B. roseni and B. terrabensis (sister species) from predator and predator free habitats, respectively. We found that in each lineage, shape differed between predation environments, consistent with the hypothesis that locomotor function is optimized for either steady swimming (predator free) or escape behavior (predator). Although differences in body shape were greatest between B. roseni and B. terrabensis, we found that much of the total morphological diversification between these species had already been achieved within B. rhabdophora (29% in females and 47% in males). Interestingly, at both levels of divergence we found that early in ontogenetic development, females differed in shape between predation environments; however, as females matured, their body shapes converged on a similar phenotype, likely due to the constraints of pregnancy. Finally, we found that body shape varies with body size in a similar way, regardless of predation environment, in each lineage. Our findings are important because they provide evidence that the same source of selection can drive similar phenotypic divergence independently at multiple divergence levels.

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Least Square Means of Relative Warps.Graph of least square means of relative warp (RW) scores (±SE) for Brachyrhaphis roseni (•), B. terrabensis (▾), B. rhabdophora from predator environments (▪), and B. rhabdophora from predator free environments (▴). Filled symbols represent males, and open symbols represent females. Female body shape converges relative to male body shape in B. roseni, B. terrabensis and populations of B. rhabdophora from divergent predation environments.
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pone-0090274-g002: Least Square Means of Relative Warps.Graph of least square means of relative warp (RW) scores (±SE) for Brachyrhaphis roseni (•), B. terrabensis (▾), B. rhabdophora from predator environments (▪), and B. rhabdophora from predator free environments (▴). Filled symbols represent males, and open symbols represent females. Female body shape converges relative to male body shape in B. roseni, B. terrabensis and populations of B. rhabdophora from divergent predation environments.

Mentions: Given that in both of our taxonomic contrasts we found a significant interaction between predation environment, sex, and the index variable in the MANOVA, we applied a phenotypic change vector analysis (PCVA; [78]–[80]) to determine the specific nature of the interaction to test for differences in shape changes between sexes. This analysis has been used previously and effectively in another Brachyrhaphis species [6]. The PCVA tests whether the significant interaction between main effects and the index variable resulted from differences in magnitude (MD) or direction (Θ) of morphological change. The PCVA tests magnitude and direction across all relative warps. Specifically, we used the PCVA to compare the amount and direction of sexual dimorphism between B. roseni and B. terrabensis, and between populations of B. rhabdophora from different predation environments. Here, we compared both size and direction of the phenotypic trajectories to test for differences in magnitude of sexual dimorphism and for different effects of predation on males and females (i.e., to determine if predation affects sexes differently), respectively. We conducted the PCVA using ASREML-R version 3.00 [75] within R (R Core Development Team 2010). We plotted LS means on the first two relative warp axes, which accounted for 64.36% of the shape variation, to visualize differences in magnitude and direction of shape change (Fig. 2).


Morphological divergence driven by predation environment within and between species of Brachyrhaphis fishes.

Ingley SJ, Billman EJ, Belk MC, Johnson JB - PLoS ONE (2014)

Least Square Means of Relative Warps.Graph of least square means of relative warp (RW) scores (±SE) for Brachyrhaphis roseni (•), B. terrabensis (▾), B. rhabdophora from predator environments (▪), and B. rhabdophora from predator free environments (▴). Filled symbols represent males, and open symbols represent females. Female body shape converges relative to male body shape in B. roseni, B. terrabensis and populations of B. rhabdophora from divergent predation environments.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3936007&req=5

pone-0090274-g002: Least Square Means of Relative Warps.Graph of least square means of relative warp (RW) scores (±SE) for Brachyrhaphis roseni (•), B. terrabensis (▾), B. rhabdophora from predator environments (▪), and B. rhabdophora from predator free environments (▴). Filled symbols represent males, and open symbols represent females. Female body shape converges relative to male body shape in B. roseni, B. terrabensis and populations of B. rhabdophora from divergent predation environments.
Mentions: Given that in both of our taxonomic contrasts we found a significant interaction between predation environment, sex, and the index variable in the MANOVA, we applied a phenotypic change vector analysis (PCVA; [78]–[80]) to determine the specific nature of the interaction to test for differences in shape changes between sexes. This analysis has been used previously and effectively in another Brachyrhaphis species [6]. The PCVA tests whether the significant interaction between main effects and the index variable resulted from differences in magnitude (MD) or direction (Θ) of morphological change. The PCVA tests magnitude and direction across all relative warps. Specifically, we used the PCVA to compare the amount and direction of sexual dimorphism between B. roseni and B. terrabensis, and between populations of B. rhabdophora from different predation environments. Here, we compared both size and direction of the phenotypic trajectories to test for differences in magnitude of sexual dimorphism and for different effects of predation on males and females (i.e., to determine if predation affects sexes differently), respectively. We conducted the PCVA using ASREML-R version 3.00 [75] within R (R Core Development Team 2010). We plotted LS means on the first two relative warp axes, which accounted for 64.36% of the shape variation, to visualize differences in magnitude and direction of shape change (Fig. 2).

Bottom Line: Natural selection often results in profound differences in body shape among populations from divergent selective environments.Interestingly, at both levels of divergence we found that early in ontogenetic development, females differed in shape between predation environments; however, as females matured, their body shapes converged on a similar phenotype, likely due to the constraints of pregnancy.Finally, we found that body shape varies with body size in a similar way, regardless of predation environment, in each lineage.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, Brigham Young University, Provo, Utah, United States of America.

ABSTRACT
Natural selection often results in profound differences in body shape among populations from divergent selective environments. Predation is a well-studied driver of divergence, with predators having a strong effect on the evolution of prey body shape, especially for traits related to escape behavior. Comparative studies, both at the population level and between species, show that the presence or absence of predators can alter prey morphology. Although this pattern is well documented in various species or population pairs, few studies have tested for similar patterns of body shape evolution at multiple stages of divergence within a taxonomic group. Here, we examine morphological divergence associated with predation environment in the livebearing fish genus Brachyrhaphis. We compare differences in body shape between populations of B. rhabdophora from different predation environments to differences in body shape between B. roseni and B. terrabensis (sister species) from predator and predator free habitats, respectively. We found that in each lineage, shape differed between predation environments, consistent with the hypothesis that locomotor function is optimized for either steady swimming (predator free) or escape behavior (predator). Although differences in body shape were greatest between B. roseni and B. terrabensis, we found that much of the total morphological diversification between these species had already been achieved within B. rhabdophora (29% in females and 47% in males). Interestingly, at both levels of divergence we found that early in ontogenetic development, females differed in shape between predation environments; however, as females matured, their body shapes converged on a similar phenotype, likely due to the constraints of pregnancy. Finally, we found that body shape varies with body size in a similar way, regardless of predation environment, in each lineage. Our findings are important because they provide evidence that the same source of selection can drive similar phenotypic divergence independently at multiple divergence levels.

Show MeSH
Related in: MedlinePlus