Article

The evolution of trade-offs: Effects of inbreeding on fecundity relationships in the cricket Gryllus firmus

Department of Biology, McGill University, Montreal, Quebec, Canada.
Evolution (Impact Factor: 4.66). 02/2001; 55(1):111-21. DOI: 10.1111/j.0014-3820.2001.tb01277.x
Source: PubMed

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.

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    • "This trade-off has been particularly well documented in G. firmus. Previous studies have revealed that: (1) micropterous (short-winged, SW) females have greatly reduced dorsolongitudinal muscles (the major flight muscles , abbreviated as DLM) relative to macropterous (long-winged, LW) females (Roff 1989; Zera et al. 1997); (2) the majority of LW females histolyse their DLM sometime during the first two weeks after their molt into the adult form (Fairbairn and Roff 1990; Stirling et al. 2001); (3) SW females show an earlier onset of reproduction and a greater reproductive output than LW females (Roff 1984, 1989, 1994); (4) The fecundity of LW females is itself negatively correlated with the condition of the DLM measured in terms of degree (complete, partial, or none) of histolysis (Roff 1989, 1994; Stirling et al. 1999), muscle mass (Roff and DeRose 2001; Roff and Gelinas 2003), and muscle color (Stirling et al. 2001); (5) Both pedigree analysis (Roff 1994; 1997; Roff and Fairbairn 2011) and selection experiments (Roff et al. 1999; Stirling et al. 2001) have demonstrated significant negative phenotypic and genetic correlations between fecundity and the condition of the DLM. Selection for increased proportion LW has also shown a correlated decrease in histolysis of the DLM and increase in the flight propensity of individuals with functional DLM (Fairbairn and Roff 1990). "
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    • "Consequently, genetic bottlenecking and subsequent impoverishment can have detrimental consequences on the fitness of once genetically diverse populations (e.g. Keller et al., 1994; Saccheri et al., 1996, 1998; Madsen et al., 1999; Bijlsma et al., 2000; Keller and Waller, 2002; Újvári et al., 2002), as for example reduced fecundity (Roff and DeRose, 2001) and/or reduced body size (Whitlock, 1993). However, this perception of Conservation Genetics is so far mostly restricted to the intraspecific level and, therefore, has to be completed by the interspecific level for a more comprehensive understanding of the importance of genetic diversity and differentiation . "
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    • "Inbreeding depression varies among insect taxa and it may be expressed as detrimental changes in egg-hatching rate (Morjan et al. 1999; Armbruster et al. 2000; van Oosterhout et al. 2000; Haikola et al. 2001; Nieminen et al. 2001; Fox and Scheibly 2006), juvenile survival (Armbruster et al. 2000; van Oosterhout et al. 2000; Haikola et al. 2001; Nieminen et al. 2001; Fox and Scheibly 2006), development time (Roff 1998; Morjan et al. 1999; Fox and Scheibly 2006), size at maturity, and increased developmental instability (Roff 2002; Reale and Roff 2003). In the adult stage, inbreeding may have detrimental effects on female fecundity (Henter 1993; Roff 1998; van Oosterhout et al. 2000; Roff and DeRose 2001), male fertility (Saccheri et al. 1996, 2005), mating behavior, sperm competition or mating success (Haikola et al. 2001; Joron and Brakefield 2003), and life span (Henter 1993; van Oosterhout et al. 2000). Inbreeding depression is assumed to be pronounced under stressful conditions (e.g., Crnokrak and Roff 1999), but empirical evidence is mixed (Armbruster and Reed 2005). "
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