Shape variation in the least killifish: ecological associations of phenotypic variation and the effects of a common garden

Abstract

Studies of the adaptive significance of variation among conspecific populations often focus on a single ecological factor. However, habitats rarely differ in only a single ecological factor, creating a challenge for identifying the relative importance of the various ecological factors that might be maintaining local adaptation. Here we investigate the ecological factors associated with male body shape variation among nine populations of the poeciliid fish, Heterandria formosa, from three distinct habitats and combine those results with a laboratory study of three of those populations to assess the contributions of genetic and environmental influences to shape variation. Field‐collected animals varied principally in three ways: the orientation of the gonopodium, the intromittent organ; the degree of body depth and streamlining; and the shape of the tail musculature. Fish collected in the spring season were larger and had a more anteriorly positioned gonopodium than fish collected in autumn. Fish collected from lotic springs were larger and more streamlined than those collected from lentic ponds or tidal marshes. Some of the variation in male shape among populations within habitats was associated with population‐level variation in species richness, adult density, vegetative cover, predation risk, and female standard length. Population‐level differences among males in body size, position of the gonopodium, and shape of the tail musculature were maintained among males reared in a common environment. In contrast, population variation in the degree of streamlining was eliminated when males were reared in a common environment. These results illustrate the complicated construction of multivariate phenotypic variation and suggest that different agents of selection have acted on different components of shape.

Unique maternal and environmental effects on the body morphology of the Least Killifish, Heterandria formosa

“…The difference between the populations increased with age. This result matches field observations and a previous common garden experiment (Landy & Travis, 2015) and reflects patterns observed in other comparisons of fish populations between high-and low-predation environments or lentic and lotic environments (Hendry, Kelly, Kinnison, & Reznick, 2006;Langerhans, 2010;Langerhans, Layman, Shokrollahi, & DeWitt, 2004).…”

“…The variation in body size at maturity and shape of the tail musculature (RW3) between males from TP and WR has an unambiguous genetic basis. This conclusion is suggested by the data from this experiment, in which the average differences between males from the different populations were robust to environmental variation, as well as data from earlier experiments that examined size at maturity at varying densities (Leips et al, 2000) and water types (Hale & Travis, 2015) and size and shape variation in a common garden (Landy & Travis, 2015). The patterns of tail musculature in H. formosa match those seen in many other studies of populations in environments with different flow or predation regimes.…”

“…The patterns of tail musculature in H. formosa match those seen in many other studies of populations in environments with different flow or predation regimes. While we cannot conclude decisively if the lotic‐lentic contrast or the high‐ and low‐predation contrast between these two individual populations is responsible for these differences, our prior field survey of nine populations, including these two populations (Landy & Travis, ), identified predation pressure as a strong predictor of tail‐shape variation independently of the lotic‐lentic contrast.…”

“…Changes in these traits after maturity combined with differences in male survival among populations could account for differences in morphology among populations. TP males experience a higher rate of predation than males in WR (Landy & Travis, ; MacRae & Travis, ). However, the presence of an asymptote in the change of size and shape after maturity suggests that postmaturation changes in body shape and size do stop and at this point population differences persist.…”

“…Prior results from a common garden study indicated that morphological variation among three populations of H. formosa was, in part, genetically based (Landy & Travis, ). However, these results may not be robust.…”