Repeatability of egg size in two marine gastropods: brood order and female size do not contribute to intraspecific variation

Abstract

Egg size has been shown to vary among females in many species of marine invertebrates and fishes. Usually, however, only a single reproductive event is measured for each female, leaving open the possibility that egg size could vary significantly among broods from the same female. Here I measured egg size from 3 to 7 broods per female from 2 calyptraeid species, Crepidula atrasolea and C. ustulatulina, in 2 experiments. In a preliminary experiment, females were raised from hatching under constant temperature in incubators; in a second larger experiment, they were raised under varying temperatures on the laboratory bench top. Under both conditions, there were significant differences in egg size among broods from each female, as well as significant differences among females from the bench top. Estimates of repeatability, which give an upper boundary on the heritability of a trait, were significantly reduced when among brood variation was included in the calculations, suggesting that caution should be used in interpreting among-female components of variation in studies that measure only a single brood per female. Egg size was not related to female size, and there was an effect of brood order on egg size in only C. ustulatulina from the bench top. Eggs produced in the incubators were larger than those from the bench top and they were more variable within broods, resulting in a lower repeatability of egg size from incubator animals than from bench top animals. The significant variation in egg size at all levels of the analysis suggests that such variation should be included in models of egg size evolution, and that the evolutionary dynamics of egg size may be more complicated than reflected in current models of life-history evolution. KEY WORDS: Crepidula · Direct development · Phenotypic plasticity · Bet-hedgingResale or republication not permitted without written consent of the publisher

Temperature-mediated trade-offs and changes in life-history integration in two slipper limpets (Gastropoda: Calyptraeidae) with planktotrophic development

“…In the two species of Crepidula with planktotrophic development examined in the present study, significant variation in egg size and hatching size was a result of the effects of temperature and maternal identity. Consistent with previous studies of Crepidula with large eggs (Collin, 2010; Collin & Salazar, 2010) and other studies of marine invertebrates (Moran & McAlister, 2009), these two species showed decreased egg size and hatching size with increasing temperature. A large proportion of the observed variation was a result of differences among females (see below).…”

“…Therefore, it is not surprising that variation among females is common (e.g. echinoids: Lessios, 1987; Berger & Jelinski, 2008; bivales: Phillips, 2007; gastropods: Collin, 2010). Lessios (1987) found significant differences in egg size between females in each of 13 species of tropical echinoids that were spawned immediately after collection.…”

“…When broods from a single female vary, the among‐female component of variation can be considerably overestimated if only a single brood is examined. For example, when multiple broods were measured for C. atrasolea and C. ustulatulina raised in incubators at the same temperatures, approximately 40% of the variation in egg size was a result of variation among broods from the same female (Collin, 2010). A similar allocation of variation in egg size and hatching size was observed in the present study: 40–50% of variation was a result of among brood variation, whereas 15–25% was a result of variation among females in C. incurva and C .…”

“…The number of days to hatching and the number of days between hatching and the deposition of the subsequent brood were recorded where possible. Ten to 20 eggs and hatchlings were photographed and measured with IMAGE J (Abramoff, Maelhaes & Ram, 2004) for three broods from each female in acordance with methods described by Collin & Salazar (2010) and Collin (2010). Because veliger shells are plan‐spiral in lateral outline, a plug‐in was designed to measure the Feret's diameter (the longest axis of the object), which is approximately equivalent to shell length as traditionally measured for gastropod larvae.…”

Seasonal Variations in Maternal Provisioning of Crepidula fornicata (Gastropoda): Fatty Acid Composition of Females, Embryos and Larvae

“…fornicata , but it has been shown that egg size and energy content may vary with brood order (e.g. [82,83]). Last, temperature might also influence maternal provisioning as has been shown through variations in egg size and hatching size in other calyptraeid species [84].…”