<p class="HeadingRunIn"><strong>Variable modes of larval development in the <em>Polydora cornuta</em> complex (Polychaeta: Spionidae) are directly related to stored sperm availability</strong></p>

Abstract

Reproductive crosses between geographically separated populations of the nominal species, Polydora cornuta, support the hypothesis that the Florida/ Gulf of Mexico populations represent a single, potentially interbreeding lineage that is reproductively isolated from West Coast (California) and East Coast (Carolinas to Maine) populations. Previous research has indicated that California populations are reproductively compatible with worms from North Carolina but reproductively isolated from Maine populations. In spite of these species-level differences, all populations of this nominal species deposit egg capsules inside the female’s tube that usually develop into three-chaetiger planktonic larvae measuring about 200 µm in length. Although adelphophagy (feeding upon unfertilized eggs within an egg capsule) has been reported in some populations of P. cornuta and in numerous other spionid polychaetes, the relationship between stored sperm in the female parent and the size of larvae within capsules has not been explored. We raised isolated female P. cornuta from three genetically and reproductively distinct populations (Florida, California and Maine) over a period of about 16 weeks and determined percent fertilization and larval size in successive spawnings over time until the females ran out of stored sperm. As each female used up stored sperm during successive spawnings, the percent of fertilized eggs per capsule declined and larval size at release increased. In some cases, the largest larvae produced by an isolated female were 114% larger than the smallest larvae produced by the same female. Larvae inside capsules containing unfertilized eggs fed upon these eggs and grew larger than larvae that did not have unfertilized eggs to feed upon. The effects of producing larger larvae following stored sperm depletion were completely reversed by transfer of fresh spermatophores to the isolated females. Variable larval size produced by a single female worm (poecilogony) may therefore be a result of stored sperm limitations rather than a genetically determined reproductive strategy in this species complex.

And then there was one:Polydora uncinataandPolydora hoplura(Annelida: Spionidae), the problematic polydorid pest species represent a single species

“…There is, however, increasing evidence demonstrating the flexibility in larval developmental mode in polydorids. For example, an increase in nurse egg production accompanied by a decrease in numbers of adelphophagic larvae per brood occurred in response to sperm limitation in Polydora cornuta (Rice & Rice, 2009) or an increase in latitude for Boccardia proboscidea (Oyarzun et al , 2011) while the opposite effect occurred when female B. proboscidea were exposed to bisphenol A (Hart et al , in Gibson et al , 2012). It is therefore possible that the poecilogony demonstrated by David et al (2014) and Simon (2015) was induced by environmental conditions unique to South Africa.…”

The effects of nurse eggs and sibling interactions on the larval development of the poecilogonous annelid Boccardia proboscidea (Spionidae)

“…In addition to the differences that we found on feeding capacities among larvae, which allow Type A larvae to advance in development inside a capsule and hatch as juveniles, the presence of greater numbers of nurse eggs could potentially reduce the probabilities of cannibalism on Type B larvae, increasing their chances of hatching as planktotrophs. According to Smith & Gibson (1999) and Gibson et al (2012), production of nurse eggs in B. proboscidea and P. cornuta form through an active process that resembles apoptosis (but see Rice & Rice 2009). Females of B. proboscidea therefore have the potential to adjust the proportion of larvae that will hatch as advanced larvae or juveniles versus larvae that will hatch as planktotrophs by manipulating the number of nurse eggs inside capsules, or by limiting the ingestion of nurse eggs and siblings by adjusting the hatching time (Oyarzun & Strathmann 2011).…”

“…According to Smith & Gibson () and Gibson et al. (), production of nurse eggs in B. proboscidea and P. cornuta form through an active process that resembles apoptosis (but see Rice & Rice ). Females of B. proboscidea therefore have the potential to adjust the proportion of larvae that will hatch as advanced larvae or juveniles versus larvae that will hatch as planktotrophs by manipulating the number of nurse eggs inside capsules, or by limiting the ingestion of nurse eggs and siblings by adjusting the hatching time (Oyarzun & Strathmann ).…”

“…In addition to food supply, two other factors have been suggested as possible mechanisms determining different developmental modes in poecilogonous species. First, Rice & Rice () raised females of the poecilogonous spionid Polydora cornuta Bosc 1802 in isolation over a period of 16 weeks. They found that as time progressed, the number of fertilized embryos declined, that the remaining larvae ate the unfertilized embryos, and therefore that hatching size of larvae increased.…”

Invasive polychaete Boccardia proboscidea Hartman, 1940 (Polychaeta: Spionidae) in sewage‐impacted areas of the SW Atlantic coasts: morphological and reproductive patterns

“…Rasmussen (1973) found that differences in the development pattern of Pygospio elegans Clapar ede were related to environmental factors and were not genetically inherent in a population. In populations of Polydora cornuta complex, the variability in larval size results from the limitations concerning the level of stored sperm in seminal receptacles of the female, rather than being a genetically determined reproductive strategy (Rice & Rice 2009). Type II: capsules of eggs with only adelphophagic larvae; Type III: capsules of eggs with both kinds of larvae.…”