Environmental and genetic components of variation in sexual allocation by an epialgal bryozoan

Abstract

Celleporella hyalina colonies growing on Fucus serratus were collected from the field and induced to release larvae in the laboratory. From these larvae, colonies were established on glass slides and each cloned by fragmentation. Growth and sexual activity of genotypic replicates in each of 4 environments were monitored for 12 wk. The environments, representing seasonal contrasts in the field, were created from the 4 combinations of lower/higher temperature and lower/higher food supply. Growth, measured as the production of basal autozooids (responsible for feeding), and sexual activity, measured separately as the production of basal male, frontal male and female zooids, were significantly affected by genotype and environment. Genotypes differed in colonial growth rate and in the numbers of male and female zooids produced per colony. Within genotypes, growth was fastest at higher temperature and food supply. Higher food supply encouraged the production of autozooids and sexual zooids. Higher temperature strongly encouraged female production, but not male. Male production was greatest at higher food supply combined with lower temperature, when female production was very low. Colonies maturing in 'summer' conditions therefore invested heavily in females whereas those maturing in 'winter' conditions invested heavily in males. This phenotypic response might promote fitness by ensuring that quantities of females are not produced under environmental conditions that would prolong embryogenesis and brooding beyond a critical time limit set by risks of colonial mortality. On the other hand, overlapping generations and sperm storage would provide opportunity for cross fertilization even dunng winter, when it would pay to invest in males. The genetically based component of variation in sexual allocation in C. hyabna may reflect polymorphism sustained by varylng mating opportunities.

Patterns of self compatibility, inbreeding depression, outcrossing, and sex allocation in a marine bryozoan suggest the predominating influence of sperm competition

“…Accordingly, Gilia achilleifolia economizes on male function and produces larger fruit when selfing, consistent with redirection of resources to female function (Schoen, 1982). In the case of C. hyalina, however, experimental evidence of a sex allocation trade off is tenuous (Hunter & Hughes, 1995), although geometrical considerations suggest that such a trade off must exist (McCartney, 1997). Sexual zooids lack trophic apparatus and depend on translocation of metabolites from trophic zooids, with this being particularly critical for the prolonged, energetically expensive, process of placental brooding (Manríquez, 1999).…”

Lessons in modularity: the evolutionary ecology of colonial invertebrates

“…Although exogenous control has been widely studied, e.g. the influence of temperature and food supply on budding rate and sexual development of bryozoan colonies (Hunter and Hughes, 1995), less attention has been paid to the technologically more challenging endogenous control, notwithstanding the pioneering studies by Braverman and Schrandt (1965), Blackstone (1997Blackstone ( ,1999 and Buss (2001). Yet characterizing endogenous controlling mechanisms and their interaction with exogenous factors is crucial for advancing beyond the scope of previous, essentially descriptive, models of astogeny.…”

Independent evolution of matrotrophy in the major classes of Bryozoa: transitions among reproductive patterns and their ecological background

“…Multiple male sperm donors and the likelihood of sperm storage could represent a source of genotypic diversity, possibly advantageous in patchy or temporally variable environments (Bernasconi et al 2004). Mothers may engage in cryptic selection through differential allocation of both resources and male genotypes, increasing their own lifetime fitness, possibly by contributing more to EEN when times are good and favoring flexibility or reduction in matrotrophic allocation in certain unfavorable times (Hunter & Hughes 1995). Offspring, in their own 'self-interest' could be selected for deriving maximum nourishment from their mothers, consistent with evolutionary transitions toward greater EEN.…”