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.
"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). "
[Show abstract][Hide abstract] ABSTRACT: Using quantitative genetic theory, we develop predictions for the evolution of trade-offs in response to directional and correlational selection. We predict that directional selection favoring an increase in one trait in a trade-off will result in change in the intercept but not the slope of the trade-off function, with the mean value of the selected trait increasing and that of the correlated trait decreasing. Natural selection will generally favor an increase in some combination of trait values, which can be represented as directional selection on an index value. Such selection induces both directional and correlational selection on the component traits. Theory predicts that selection on an index value will also change the intercept but not the slope of the trade-off function but because of correlational selection, the direction of change in component traits may be in the same or opposite directions. We test these predictions using artificial selection on the well-established trade-off between fecundity and flight capability in the cricket, Gryllus firmus and compare the empirical results with a priori predictions made using genetic parameters from a separate half-sibling experiment. Our results support the predictions and illustrate the complexity of trade-off evolution when component traits are subject to both directional and correlational selection.
"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 . "
[Show abstract][Hide abstract] ABSTRACT: In general, species with large ecological amplitudes are equipped with high genetic diversities. In contrast, more specialised species with narrow ecological amplitudes show low levels of genetic diversity. Generalist species are mostly rather marginally affected by recent land-use changes; specialist can be supported by specific conservation measures. We argue that, in the light of Conservation Genetics, species being ecologically intermediate between these two extremes are the most seriously affected ones by recent environmental changes. Such species which formerly occurred in large population networks have to sustain their high level of genetic variability via gene flow. Today, species from the latter group are negatively affected by rapid habitat collapses causing sudden lacks of population interconnectivity. Therefore, species with intermediate habitat demands and originally high genetic diversity might be at highest risk due to inbreeding depressions.
"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). "
[Show abstract][Hide abstract] ABSTRACT: Inbreeding depression is a relative decline in fitness in offspring of related parents. The magnitude of inbreeding costs
varies among taxa and may increase under stressful conditions. Inbreeding tolerance is expected to be low and selection for
inbreeding avoidance intense when both sexes invest substantially in shared offspring like in nuptial gift-giving butterflies.
This is especially true for increasing mating rate for inbreeding avoidance as nuptial feeding decreases net costs of mating
for females. We explored implications of inbreeding in the nuptial gift-giving green-veined white butterfly, Pieris napi. Compared to outbred ones, partially inbred (F = 0.25) eggs and neonate larvae had 25% lower hatching success and 30% lower survival until adult eclosion, respectively.
Inbreeding was also associated with small size. Yet, the magnitude of inbreeding depression was independent of larval conditions.
A lack of assortative mating and mating durations independent of mating type suggest that neither females nor males discriminate
close relatives (r = 0.5) as mates. Indicative of a postcopulatory mechanism to avoid inbreeding, female remating intervals decreased following
incestuous matings. Such a plastic response may affect the level of postcopulatory sexual selection as female remating interval
(time between successive matings) is necessarily negatively correlated with mating rate (matings per unit time) and mating
frequency (lifetime number of matings), and precopulatory mate choice appeared insignificant. Moreover, incest-induced shift
in the phenotype towards the adaptive peak may contribute to the evolution of female mating rates, although alternative explanations
for polyandry besides material benefits have rarely been invoked when nuptial feeding is involved.
–Phenotypic plasticity–Nuptial feeding–Postcopulatory sexual selection
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