Quantitative Genetic Variation in Static Allometry in the Threespine Stickleback

Abstract

The common pattern of replicated evolution of a consistent shape-environment relationship might reflect selection acting in similar ways within each environment, but divergently among environments. However, phenotypic evolution depends on the availability of additive genetic variation as well as on the direction of selection, implicating a bias in the distribution of genetic variance as a potential contributor to replicated evolution. Allometry, the relationship between shape and size, is a potential source of genetic bias that is poorly understood. The threespine stickleback, Gasterosteus aculeatus, provides an ideal system for exploring the contribution of genetic variance in body shape allometry to evolutionary patterns. The stickleback system comprises marine populations that exhibit limited phenotypic variation, and young freshwater populations which, following independent colonization events, have often evolved similar phenotypes in similar environments. In particular, stickleback diversification has involved changes in both total body size and relative size of body regions (i.e., shape). In a laboratory-reared cohort derived from an oceanic Alaskan population that is phenotypically and genetically representative of the ancestor of the diverse freshwater populations in this region, we determined the phenotypic static allometry, and estimated the additive genetic variation about these population-level allometric functions. We detected significant allometry, with larger fish having relatively smaller heads, a longer base to their second dorsal fin, and longer, shallower caudal peduncles. There was additive genetic variance in body size and in size-independent body shape (i.e., allometric elevation), but typically not in allometric slopes. These results suggest that the parallel evolution of body shape in threespine stickleback is not likely to have been a correlated response to selection on body size, or vice versa. Although allometry is common in fishes, this study highlights the need for additional data on genetic variation in allometric functions to determine how allometry evolves and how it influences phenotypic evolution.

Plasticity and heritability of morphological variation within and between parapatric stickleback demes

“…, 2011). And although McGuigan et al. (2010) have shown that evidence of allometry alone does not predict a correlated response to selection between growth/size and body form, it is generally assumed that allometry is ultimately pleiotropic in nature (Klingenberg, 2010).…”

Data from: Ancestral plasticity and allometry in threespine stickleback reveal phenotypes associated with derived, freshwater ecotypes

“…However, available evidence suggests that Rabbit Slough stickleback harbor little to no additive genetic variance in the slope of static allometry (the relationship between size and shape among individuals of the same age; McGuigan et al, 2010b), so additive variance in the slopes of ontogenetic allometry (allometries of individuals of different ages/sizes) is likely not present, since the latter leads to the former (Shingleton et al, 2007). Allometry, and the expression of genetic variance thereof, might be environmentally contingent.…”

Iterative development and the scope for plasticity: contrasts among trait categories in an adaptive radiation

“…Plastic influences on morphological phenotypes are more apparent in continuously varying characters including body size, body shape and gill raker morphology (Day et al, 1994;Wund et al, 2008McCairns and Bernatchez, 2010, although genetic variation is a primary determinant of variation in expression of these traits (Peichel et al, 2001;Aguirre et al, 2004;Albert et al, 2008;McGuigan et al, 2010;Berner et al, 2014). Factors such as diet, habitat structure, water velocity and salinity vary considerably among populations, and all are known to impact the development of these features in stickleback and/ or other fishes (Day et al, 1994;Pakkasmaa and Piironen, 2000;Imre et al, 2002;McCairns and Bernatchez, 2012;Wund, 2012).…”