Ontogeny and sex alter the effect of predation on body shape in a livebearing fish: sexual dimorphism, parallelism, and costs of reproduction

Abstract

Predation can cause morphological divergence among populations, while ontogeny and sex often determine much of morphological diversity among individuals. We used geometric morphometrics to characterize body shape in the livebearing fish Brachyrhaphis rhabdophora to test for interactions between these three major shape-determining factors. We assessed shape variation between juveniles and adults of both sexes, and among adults for populations from high- and low-predation areas. Shape differed significantly between predation regimes for all juveniles regardless of sex. As males grew and matured into adults, ontogenetic shape trajectories were parallel, thus maintaining shape differences in adult males between predation environments. However, shape of adult females between predation environments followed a different pattern. As females grew and matured, ontogenetic shape trajectories converged so that shape differences were less pronounced between mature females in predator and nonpredator environments. Convergence in female body shape may indicate a trade-off between optimal shape for predator evasion versus shape required for the livebearing mode of reproduction.

Urbanization drives contemporary evolution in stream fish

“…We log 10 ‐transformed centroid size to improve normality of residuals. We used site nested within urbanization status (urban or rural) as a random effect (see Hassell, Meyers, Billman, Rasmussen, and Belk (), Heinen‐Kay and Langerhans () and Riesch, Martin, and Langerhans () for other examples of this statistical approach). The p ‐value for the effect of urbanization was determined using the MIXED procedure in SAS in order to treat populations as random effects (appropriate since population serves as the unit of replication for this test of urbanization status).…”

Intraspecific Morphological Variation in Two Common Marine Fish Species from South Africa

“…In a multivariate mixed model design, relative warps are treated as repeated measures within individuals, thus individual is treated as a random variable in the analysis. Analysis was done with the MIXED procedure in SAS (SAS Enterprise Guide v. 4.3, SAS Institute Inc., Cary, NC, USA) [29,30].…”

Quantitative trait locus analysis of body shape divergence in nine-spined sticklebacks based on high-density SNP-panel

“…While common garden experiments567 can verify the heritable nature of such divergence, uncovering the genetic basis of these complex phenotypic traits can be far more challenging89. For instance, adaptive genetic divergence in body shape among fish populations residing in different environments has been repeatedly demonstrated101112, but the genetic underpinnings of this divergence are still fairly poorly understood1314. This is not surprising, because body shape is a complex trait, likely to be highly polygenic: large sample sizes, both in terms of number of individuals and markers, are needed to identify the causal loci influencing variation in such traits1516.…”