Sex Ratio, Parental Investment, and Interparent Variability in Nesting Success in a Solitary Bee

Abstract

Observations of uniquely marked females of the solitary, twig-nesting bee, Osmia bruneri, were conducted under greenhouse conditions to test several predictions of sex-ratio and parental-investment theory. In support of Fisher's (1958) theory, we found that the observed sex-ratio of progeny in this dimorphic species did not differ from that expected on the basis of average male and female weights. Investment patterns also exhibited a seasonal component: female parents produced more female than male offspring early in the nesting season but reversed this pattern later. Interfemale variability was large for all nesting parameters examined. Neither female-parent size nor the rate at which females completed cells was significantly related to several estimates of parent fitness. Parent-offspring heritability for size was also low. We found no evidence to support the hypothesis that progeny sex-ratios are influenced by maternal condition. Variance in progeny sex-ratios was large, but the population sex-ratio probably departs frequently from the equilibrium value. The results marginally support Kolman's (1960) prediction of large variance in progeny sex-ratios in large panmictic populations. We conclude that variability among females in investment patterns and variability in size among progenies are probably maintained by such factors as resource heterogeneity and the shape of the adult survivorship curve.

Sex ratios and life-history patterns of a solitary wasp, Trypoxylon (Trypargilum) politum (Hymenoptera : Sphecidae)

“…A 1 : 1 equilibrium sex ratio is expected only when sons and daughters cost the same to produce. Since male pipe-organ muddaubers are smaller than females, one expects a somewhat male-biased numerical sex ratio that is proportional to the relative investment (Howe 1976;Maynard Smith 1978;Torchio and Tepedino 1980;Frohlich and Tepedino 1986;Johnson 1988). One needs to know a great deal about the biology of the organism, however, if one is to measure investment properly (Danforth 1990).…”

Sex ratio and parental investment in Trypoxylon (Trypargilum) agamemnon Richards (Hymenoptera, Crabronidae)

“…For many massprovisioning wasps, the weight of provision per cell is a good predictor of each offspring's cost to the mother (Cowan, 1981;Frohlich and Tepedino, 1986), and body size of these insects is correlated with the amount of provisions in each cell (Brockmann and Grafen, 1989;Cowan, 1981). This amount may be influenced by such factors as hunting success, prey availability, species interactions and the size of the brood cell (Lin, 1979).…”

Alocação sexual e seleção sexo-dependente para tamanho de corpo em Trypoxylon rogenhoferi Kohl (Hymenoptera, Sphecidae)

“…Porém, em himenópteros aculeados (abelhas, formigas e algumas vespas) há desvios desta proporção, freqüentemente atribuídos a fatores ecológicos, fisiológicos e comportamentais. Entender a natureza e evolução destes desvios é um dos objetivos de estudos sobre a evolução da socialidade em Hymenoptera (TRIVERS & HARE 1976;ALEXANDER & SHERMAN 1977;FROHLICH & TEPEDINO 1986;BROCKMANN & GRAFEN 1992;HELMS 1994;DESLIPPE & SAVOLAINEN 1995;CROZIER & PAMILO 1996;YANEGA 1996;CHAPUISAT & KELLER 1999;STROHM & LINSENMAIR 1997a, 1997bOKU & NISHIDA 1999.…”