The Evolution of Trade-Offs: Effects of Inbreeding on Fecundity Relationships in the Cricket Gryllus Firmus

Abstract

Abstract. The evolution of traits is modulated by their interrelationships with each other, particularly when those relationships result in a fitness trade-off. In this paper we explore the consequences of genetic architecture on functional relationships between traits. Specifically, we address the consequences of inbreeding on these relationships. We show that the linear regression between two traits will not be affected if there is no dominance genetic variance in either trait, whereas the intercept but not the slope of the regression will change if there is dominance genetic variance in one trait only. We test the latter hypothesis using fecundity relationships in the cricket Gryllus firmus. Data from pedigree analysis and an inbreeding experiment show that there is significant dominance genetic variance in fecundity, but not head width (an index of body size) or dorsal longitudinal muscle (DLM) mass. Fecundity increases with head width, but decreases with DLM mass. As predicted, the intercepts of the regressions of fecundity on these two morphological traits decrease with inbreeding, but there is little or no change in slope. Gryllus firmus is wing dimorphic, with the macropterous (LW) morph having a lower fecundity than the micropterous (SW) morph. We hypothesize that the difference in fecundity arises primarily because of a competition for resources in the LW females between DLM maintenance (i.e., mass) and egg production. As a consequence, we predict that the fecundity within each morph should decline linearly with the inbreeding coefficient at the same rate in both morphs. The result of this will be a change in the relative fitness of the two morphs, that of the SW morph increasing with inbreeding. This prediction is supported. These results indicate that trade-offs will evolve and such changes will affect evolutionary trajectories by altering the pattern of relationships among fitness components.

Inbreeding, Developmental Stability, and Canalization in the Sand Cricket Gryllus Firmus

“…Inbred and outbred lines originated from the same stock population and were maintained in the same environmental conditions. Inbreeding depression on weight, fecundity, and muscle mass has been found for these cricket lines (Roff 1998(Roff , 2002Roff and DeRose 2001). Shorter limbs are thus expected in inbred lines compared to crossbred or outbred lines.…”

Analysis of two components of flight using recombinant inbred lines of Drosophila melanogaster

“…Although accurate methods of testing are under development (Cheverud, 1999;Mackay, 2004), detailed information on the number and interactions of genes and the trait(s) they control is easiest to obtain from a system for which a substantial prior investigation exists. Not surprisingly, relatively fewer studies (Roff, 1996;Roff & DeRose, 2001;Montooth, Marden & Clark, 2003;Ahnholt & Mackay, 2004;Khazaeli et al, unpublished) venture into this kind of investigation.…”

“…Curtsinger and Laurie-Ahlberg (1981) were first to investigate the genetics of power output by D. melanogaster during flight. More recently, Roff and DeRose (2001) applied quantitative genetic analyses in studying flight using inbred lines of the migratory cricket Gyrillis firmus. Montooth, Marden and Clark (2003) followed with an extensive investigation of the biochemical genetics underlying power output by Drosophila, measured as peak velocity in free flight.…”

Effects of Genetic Captive-Breeding Protocols on Sperm Quality and Fertility in the White-Footed Mouse1

“…Understanding the impact of inbreeding on fecundity is central both to evolutionary biology [15] and to conservation biology [16]. During the past two decades, growing evidence has indicated the effects of inbreeding on male reproductive quality in mammals.…”