Path analysis of the genetic integration of traits in the sand cricket: a novel use of BLUPs

Abstract

This study combines path analysis with quantitative genetics to analyse a key life history trade‐off in the cricket, Gryllus firmus. We develop a path model connecting five traits associated with the trade‐off between flight capability and reproduction and test this model using phenotypic data and estimates of breeding values (best linear unbiased predictors) from a half‐sibling experiment. Strong support by both types of data validates our causal model and indicates concordance between the phenotypic and genetic expression of the trade‐off. Comparisons of the trade‐off between sexes and wing morphs reveal that these discrete phenotypes are not genetically independent and that the evolutionary trajectories of the two wing morphs are more tightly constrained to covary than those of the two sexes. Our results illustrate the benefits of combining a quantitative genetic analysis, which examines statistical correlations between traits, with a path model that focuses upon the causal components of variation.

The costs of being dark: the genetic basis of melanism and its association with fitness‐related traits in the sand cricket

“…The path analysis not only indicated a trade‐off between melanization and gonad mass, but also that the former is determined by the latter and not the reverse. One interpretation of this path direction is that individuals are preferentially allocating resources to gonad development rather than melanization, with allocation to gonads greater in SW than in LW individuals (as we have previously shown) (Roff & Fairbairn, ). Although the path analysis showed no significant direct causal links between melanization and DLM mass, the path direction between DLM mass and gonad mass suggests that resources are preferentially allocated to DLM mass, and thus, there may be an indirect effect of DLM mass on melanization via this path.…”

“…Fortunately, comparisons between the four lines used in our analyses provide a second means of testing this hypothesis. Previously, we have shown that there is a highly significant correlation between the phenotypic and genetic correlations among the pairwise combinations of wing morph, DLM mass, gonad mass and sex (Roff & Fairbairn, ). Assuming that this conclusion is also true for pairwise combinations involving melanization, we can make predictions about how melanization should have changed as an indirect response to the selection regimes imposed on the four lines.…”

“…. The symbols indicating the hypothesized sign of the path coefficients were based on the previous analysis of Roff & Fairbairn () or as rationalized in the text. Paths with “?” are ones for which the sign is uncertain.…”

Evolução morfológica no crânio de Lemuriformes (Primates:Strepsirrhini)

“…Dessa forma, investigações baseadas na teoria da genética quantitativa acerca da evolução morfológica de populações contemporâneas podem se valer de matrizes P, estimadas a partir de um tama-5 nho amostral apropriado à dimensão da matriz como substitutas de suas respectivas G (Agrawal and Stinchcombe, 2009;Oliveira et al, 2009;Porto et al, 2009;Steppan, 1997 res morfológicos e cranianos (Dochtermann, 2011;Garcia et al, 2014;Reusch and Blanckenhorn, 1998;Roff, 2012;Roff and Fairbairn, 2011;Roff, 1995) e parece se aplicar aos crânios de mamíferos (Garcia et al, 2014).…”

“…res morfológicos e cranianos (Dochtermann, 2011;Garcia et al, 2014;Reusch and Blanckenhorn, 1998;Roff, 2012;Roff and Fairbairn, 2011;Roff, 1995) e parece se aplicar aos crânios de mamíferos (Garcia et al, 2014).…”