Long-term studies in the abyssal north-east Atlantic (1989–2005) have revealed large-scale changes in the benthic ecosystem and especially in some megafaunal invertebrate taxa over the period 1996–2002, termed the ‘Amperima Event’. Holothurians dominated the megafaunal samples. Temporal patterns in the abundance of holothurians showed a wide spectrum of responses, possibly related to the feeding and reproductive characteristics of the various species. One of the holothurians, the synallactid Paroriza prouhoi, is a simultaneous hermaphrodite, providing a distinct comparison with dioecious reproductive patterns more typical of deep-sea holothurian species. The reproductive biology and abundance/biomass patterns of P. prouhoi were investigated over the period 1989–2005. Paroriza prouhoi produces oocytes with a maximum diameter of ~370 µm. It has asynchronous patterns of gametogenesis both at the individual and population levels. Mean oocyte diameter and the ratio between previtellogenic and vitellogenic oocytes showed no significant differences between the periods prior to and after the Amperima Event. There were no significant differences in abundance or biomass over the time series. We conclude that the energy investment into gamete production by this hermaphrodite did not change over the 16 years examined. It is hypothesized that the feeding characteristics of P. prouhoi lead to a slow, steady and consistent production of gametes despite large-scale changes in organic matter supply to the seabed evident at the time series locality.

Reproductive aspects of the intensively traded ornamental shrimp Lysmata boggessi were examined. Abundance, reproductive biology (fecundity, reproductive output and egg size) and population structure (frequency distribution, size at sex phase change and sex phase ratio) were examined at three different fishing grounds off south and west-central Florida between May 2011 and February 2012. Fishery-dependent densities of L. boggessi varied between 2.51 ± 1.39 and 13.05 ± 9.30 shrimps per 1000 m2 at two different localities. The proportion of brooding shrimp varied considerably at one locality during two different dates, suggesting reproductive seasonality. Reproductive output increased linearly with shrimp body weight (SBW) at one locality (May 2011), but scaled negatively with SBW at a second locality (January–February 2012). Lastly, no correlation between embryo size and shrimp carapace length (CL) was recorded at one locality (May 2011), but a slight negative correlation between embryo size and CL was found at the second locality (January–February 2012). Lysmata boggessi might be experiencing trade-offs between different reproductive parameters driven by environmental, probably seasonal, conditions during the year. All of this information needs to be considered in assessing shrimp stocks and establishing a sustainable management plan.

Sampling of commercial fisheries bycatch in south-western Australia has yielded a second and different form of hermaphrodite of the Port Jackson shark Heterodontus portusjacksoni. Its total length (706 mm) and weight (2740 g) fall within the range of those of mature males, but below those of mature females. The left clasper was similar to that of normal mature males, whereas the right clasper was far smaller, had a poorly-developed rhipidion groove and lacked a spur. The body cavity possessed a testis on the left, an ovotestis on the right, and contained sperm ducts, oviducal glands and uteri on both sides. As with normal mature males, the testis and the testicular component of the ovotestis contained germ cells in various stages of spermatogenesis, including late stage spermatids. The ovarian component of the ovotestis contained 14 follicles that were larger (5–9 mm diameter) than those of normal females of similar size, which were immature, but far smaller than those of normal mature females. Six of those follicles were atretic. The widths of the left and right oviducal glands and uteri were far greater than those of normal females of similar size, but similar to those of normal mature females. Thus, although gonadal maturation had progressed further in the testis and the testicular component of the ovotestis than in the ovarian component of the ovotestis, the oviducal glands and the uteri of the hermaphrodite were of similar size to those of normal mature females and were far better developed than those of normal females of similar length, which are immature.

The entomopathogenic nematode Heterorhabditis megidis may undergo several rounds of reproduction within a single host. Infective juveniles (IJs) are formed within each generation during a process referred to as endotokia matricida, which involves the progressive consumption of the parent hermaphrodite or female by the developing IJs prior to emergence from the host cadaver. The present study examines the extent to which within-host population dynamics exhibit density-dependent variation. Particular attention is paid to the effect of infection density on the relative production of IJs and ‘normal’, non-infective offspring within each generation and on the emergence of the IJs from the host. Fecundity was found to be negatively density dependent across generations. However, at high infection density the first generation hermaphrodites invested relatively more in IJs at the expense of producing non-infective offspring. It is suggested that this pattern resulted from an adaptive, phenotypically plastic allocation of reproductive investment between offspring types in response to increased competition. The F1 and F2 IJs were also shown to emerge from the host in relatively discrete pulses.

More than 20 species of the entomopathogenic nematode Steinernema have been described; to date, all reproduce exclusively by cross-fertilization of male and female individuals. Steinernema sp. strain T87 from Indonesia was found to consist largely of self-fertile hermaphrodites. Progeny were produced by morphological females both in insects (Galleria mellonella) and in hanging drops of insect haemolymph inoculated with a single infective juvenile. Sperm were present in the oviduct of unmated morphological females. Approximately 1% of infective juveniles developed into males, and males were also present in the second generation where they constituted 1–6% of the population. Under the same conditions the related species Steinernema longicaudum strain CB2B displayed typical steinernematid reproduction: cross-fertilization and a 1:1 sex ratio. It is argued that the development of hermaphroditism in Steinernema sp. T87 represents convergent evolution with Heterorhabditis, the other major genus of entomopathogenic nematode.

Sperm-dependent parthenogens are expected to promote higher female fecundity at the expense of the production of excessive numbers of sperm. They are also expected to trade sperm strictly, in order to compensate for the loss of nutrients invested in sperm, that otherwise could be allocated to the female function. In this paper, we present evidence that in a natural population of the freshwater planarian Girardia (= Dugesia) tigrina, sperm-dependent parthenogenesis is alternated with fissipary, a combination not reported before for freshwater flatworms. More specifically, we found that most individuals that engage in a copulation have no or only few testes and sperm available, despite the presence of a fully developed penis, indicating that male allocation is fairly low in this (dense) population. Female fecundity on the contrary is rather high, with isolated individuals producing up to six fertilized cocoons over a 3-week period, releasing five young per cocoon on average. An analysis of the mating behaviour further shows that matings in this species are simple and direct with no distinct courtship behaviour. Copulations last for about 36 min and occur at a rate of at least one copulation a day. Bilateral sperm transfer is the rule, but a considerable number of copulations are unidirectional or without sperm transfer. Non-reciprocal inseminations mainly result from the fact that one or both partners has no sperm stored prior to copulation, indicating that strict sperm trading plays no role in this population of G. tigrina.

Moulting and copulation by the barnacle Tetraclita japonica attached to an intertidal concrete pier were observed continuously with a video camera housed in a plastic case in summer 1996 and 1997. In a total of 779 individual-day observations, 10 individuals became sexually receptive as functional females and 14 moulted. Copulation occurred not only immediately after, but also before moulting. Duration of receptivity varied from 2 min to nearly 12 h, during which functional females accepted between two to 582 penis insertions by between one to 11 surrounding males. Each insertion time was short, ranging from 0.6 to 42 s, with a median of 2.4 s. Sex role changes were observed between two animals located close to each other, the shortest interval for which was 3.3 h. No significant size differences were detected between functional males and females. A temporal pattern of copulation, with a high frequency of penis insertions of short durations, is discussed in relation to natural habitat conditions.