Abstract
Animals display diverse means of producing and provisioning offspring, from eggs to embryos and juveniles. While external development predominates, many forms of embryonic incubation have evolved, including placentation in mammals and a number of understudied variants in basal metazoans that could help understand evolutionary diversification. Here we studied the brooding sea anemone Aulactinia stella, using behavioural, morphological and biochemical indicators of offspring phenotype to characterize gestation and elucidate parental and sibling relationships. The pronounced variance in juvenile weight within broods was not strongly related to any of the typical external predictors (adult weight, clutch size, sampling date, environmental conditions). Lipid concentration was significantly higher in the tissues of the small juveniles than in those of large juveniles or adult, and fatty acid profiles tended to set small juveniles apart. Finally, intra-brood feeding on external resources was documented in larger juveniles. These results are consistent with ontogenetic shifts in nutrition, from vitellogenic provisioning to post-zygotic nourishment to a prenatal form of nursing upon acquisition of feeding organs, highlighting matrotrophic and conflict-driven mechanisms acting on offspring phenotype during gestation.
Highlights
The many different ways through which animals produce and nurture their progeny have long been a source of curiosity and wonder
The present study focused on a species belonging to a basal animal phylum, the sea anemone Aulactinia stella (Cnidaria: Actiniaria), which incubates progeny in the gastrovascular cavity and releases few fully-formed benthic juveniles [16, 17]
Results from feeding trials and lipid and fatty acid analyses suggest shifts in offspring nutrition modes, from vitellogenic provisioning to extra-vitellogenic nourishment to prenatal feeding facilitated by the parent, as juveniles develop functional feeding organs
Summary
The many different ways through which animals produce and nurture their progeny have long been a source of curiosity and wonder. A continuum of strategies, from external development involving minimal parental care all the way to direct nutrient transfer across placental tissues, have been documented [1,2,3,4,5]. Evolutionary transitions towards the retention of progeny are typically interpreted to favour survival of incubated offspring [6]. Competition among siblings is most often studied in species with postnatal nursing, such as birds and mammals [9], but it may be important when parental care occurs between fertilization and birth/release [10,11,12,13].
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