Maternal Body Size as an Evolutionary Constraint on Egg Size in a Butterfly

Abstract

Genetic and developmental constraints have often been invoked to explain patterns of existing morphologies. Yet, empiricaltests addressing this issue directly are still scarce. We here set out to investigate the importance of maternal body size as an evolutionary constraint on egg size in the tropical butterfly Bicyclus anynana, employing an artificial two-trait selection experiment on simultaneous changes in body and egg size (synergistic and antagonistic selection). Selection on maternal body size and egg size was successful in both the synergistic and the antagonistic selection direction. Yet, responses to selection and realized heritabilities varied across selection regimes: the most extreme values for pupal mass were found in the synergistic selection directions, whereas in the antagonistic selection direction realized heritabilities were low and nonsignificant in three of four cases. In contrast, for egg size the highest values were obtained in the lines selected for low pupal mass. Thus, selection on body size yielded a stronger correlated response in egg size than vice versa, which is likely to bias (i.e., constrain), if weakly, evolutionary change in body size. However, it seems questionable whether this will prevent evolution toward novel phenotypes, given enough time and that natural selection is strong. Correlated responses to selection were overall weak. Egg and larval development times tended to be associated with changes in maternal size, whereas variation in pupal development times weakly tended to follow variation in egg size. Lifetime fecundity was similar across selection regimes, except for females simultaneously selected for large body mass and small egg size, exhibiting increased fecundity. Multiple regressions showed that lifetime fecundity and concomitantly reproductive investment were primarily determined by longevity, as expected for an income breeder, whereas egg size was primarily determined by pupal mass. Evidence for a phenotypic trade-off between egg size and number was weak.KEY WORDS: Antagonistic selection, artificial selection, Bicyclus anynana, fecundity, life-history evolution, reproductive investment, synergistic selection.After years of emphasizing the almost omnipotence of natural selection in shaping life histories, it is now generally acknowledged that phenotypes are not only shaped by selection, but also by constraints that limit or channel evolutionary change (Stearns 1992;Schlichting and Pigliucci 1998;Roff 2002;Beldade et al. 2002a;Brakefield 2006). Thus, life histories involve compromises between what selection can achieve (adaptation) and what selection is prevented from achieving (constraints; Barnes and Partridge 2003). Evolutionary constraints may stem from genetic or developmental interrelations among a suite of traits, and have often been invoked to explain patterns of existing morphologies (Yang 2001; Beldade et al. 2002a,b;Zijlstra et al. 2003;Frankino et al. 2005;Brakefield 2006;Griswold 2006). However, to date, empirical data testing evolutionary constraint...

Temperature and humidity acclimation increase desiccation resistance in the butterfly Bicyclus anynana

“…The general pattern of a sex difference in mass loss under food and water deprivation prevailed in both experiments, but attained significance in the thermal acclimation experiment only. The latter notion rests on the finding that female lifespan is often positively related to realised fecundity (Honek, 1993;Bauerfeind & Fischer, 2007. A higher water loss in males is presumably linked to their smaller size and a concomitantly higher surface area-to-volume ratio.…”

Response to Selection on Cold Tolerance Is Constrained by Inbreeding

“…The adults feed on a diversity of fallen and decaying fruits (Larsen 1991; Brakefield 1997). This species exhibits two seasonal morphs as an adaptation to the wet and dry season in its natural environment, and the associated changes in resting background and predation (Brakefield 1997; Lyytinen et al 2004; Bauerfeind and Fischer 2007). As morphs are gradually replaced during seasonal transitions, both phenotypes may occur simultaneously (Brakefield and Reitsma 1991).…”

“…This population in turn originated from a stock population at Leiden University (the Netherlands), which was established in 1988 from 80 gravid females caught at a single location in Malawi. Several hundred individuals are reared in each generation, maintaining high levels of heterozygosity at neutral loci (Van't Hof et al 2005; Bauerfeind and Fischer 2007).…”

“…Adults were kept in cylindrical hanging cages (30 × 38 cm), being fed on moist banana. Throughout, cages were arranged in a randomized block design within the climate cabinet in order to balance potential slight temperature and humidity variation (Bauerfeind and Fischer 2007; Fischer et al 2010).…”

“…In parallel, we test for longer lasting effects of inbreeding depression and for effects of purging, by measuring inbreeding depression in several fitness‐related traits, such as fecundity, development time, longevity, and temperature stress resistance after the course of selection. We used the tropical butterfly Bicyclus anynana (Butler, 1879) as a model organism, as it has been intensively used in studies using artificial selection and on inbreeding (e.g., Brakefield and Saccheri 1994; Saccheri et al 1996; Beldade et al 2002; Joron and Brakefield 2003; Fischer 2006; Bauerfeind and Fischer 2007; Dierks et al 2012; Prudic et al 2011).…”