Instantaneous Fecundity Research Articles

Comparative Reproductive Biology of Deep-Sea Ophiuroids Inhabiting Polymetallic-Nodule Fields in the Clarion-Clipperton Fracture Zone

Deep-sea mining in the Pacific Clarion-Clipperton Fracture Zone (CCZ), a low-energy sedimentary habitat with polymetallic nodules, is expected to have considerable and long-lasting environmental impact. The CCZ hosts extraordinarily high species diversity across representatives from all Domains of Life. Data on species biology and ecology remain scarce, however. The current study describes the reproductive biology of Ophiosphalma glabrum (Ophiosphalmidae) and Ophiacantha cosmica (Ophiacanthidae), two ophiuroids frequently found in the CCZ. Specimens collected in Spring 2015 and 2019 in four contract areas were examined morphologically and histologically. Size-class frequencies (disc diameter and oocytes feret diameters), sex ratios, gametogenic status, putative reproductive mode, and a simple proxy for fecundity are presented. Habitat use differs in each. While O. glabrum is epibenthic, occurring as single individuals, O. cosmica often forms size-stratified groups living on stalked sponges, suggesting gregarious settlement or retention of offspring (though no brooding individuals were found). Further molecular analyses are needed to establish whether O. cosmica groups are familial. In O. glabrum, for which sample sizes were larger, sex ratios approximated a 1:1 ratio with no size-structuring. In both species, individuals were at various stages of gametogenic maturity, but no ripe females were identified. Based on this, O. glabrum is most probably gonochoric. Reproductive mode remains inconclusive for O. cosmica. Both species are presumptively lecithotrophic, with vitellogenic-oocyte feret diameters exceeding 250 μm. Oocyte feret diameters at times exceeded 400 μm in O. glabrum, indicating substantial yolk reserves. Estimates of instantaneous fecundity (vitellogenic specimens of O. glabrum only) were confounded by interindividual variability in gonad characteristics. The well-furnished lecithotrophic larvae of O. glabrum would be capable of dispersing even under food-impoverished conditions. The current study examines ophiuroid reproductive biology over multiple localities in the CCZ concurrently for the first time, at sites characterised by differing productivity regimes. The reproductive biology of each species is thus discussed with reference to past evolutionary (habitat stability), contemporary (food supply), and future environmental drivers (potential impacts of deep-sea mining).

Mechanisms behind bottom-up effects: eutrophication increases fecundity by shortening the interspawning interval in stickleback

Anthropogenic eutrophication is altering aquatic environments by promoting primary production. This influences the population dynamics of consumers through bottom-up effects, but the underlying mechanisms and pathways are not always clear. To evaluate and mitigate effects of eutrophication on ecological communities, more research is needed on the underlying factors. Here we show that anthropogenic eutrophication increases population fecundity in the threespine stickleback (Gasterosteus aculeatus) by increasing the number of times females reproduce—lifetime fecundity—rather than instantaneous fecundity. When we exposed females to nutrient-enriched waters with enhanced algal growth, their interspawning interval shortened but the size of their egg clutches, or the size of their eggs, did not change. The shortening of the interspawning interval was probably caused by higher food intake, as algae growth promotes the growth of preferred prey populations. Enhanced female lifetime fecundity could increase offspring production and, hence, influence population dynamics. In support of this, earlier studies show that more offspring are emerging in habitats with denser algae growth. Thus, our results stress the importance of considering lifetime fecundity, in addition to instantaneous fecundity, when investigating the impact of human-induced eutrophication on population processes. At a broader level, our results highlight the importance of following individuals over longer time spans when evaluating the pathways and processes through which environmental changes influence individual fitness and population processes.

Temperature and salinity induce differential responses in life histories of cryptic nematode species

In the marine environment, many cryptic — morphologically similar but genetically distinct — species show sympatric distributions, which challenges traditional ecological competition theory. In the morphospecies complex of the bacterivorous nematode Litoditis marina, four cryptic species (Pm I, Pm II, Pm III and Pm IV) frequently occur with mostly two or more of these species together. This co-occurrence displays fluctuating abundances that have been linked to seasonal dynamics in the environment. In intertidal marine environments, salinity and temperature play an important role in species distributions. In the here presented experiments, the impact of these two abiotic variables on juvenile development time, fecundity and population development was investigated. Monospecific cultures were reared at three different temperatures: 15°C, 20°C and 25°C (salinity 25) and at two different salinities: 15 and 25 (temperature: 20°C) in 2 separate experiments. Our results showed that differences in life history are present between the four species: Pm III had a higher instantaneous fecundity than the other three species. Furthermore, differences in reproduction strategy were observed between the cryptic species: Pm II and Pm III were always oviparous in this experiment, whilst Pm I and Pm IV were mostly viviparous species. Abiotic factors affected the life history characters and the reproductive strategy of some of these cryptic species, with temperature clearly having a stronger effect than salinity. Temperature had an effect on juvenile development time for all species and a species-specific influence on population development. Pm III performed better at higher temperature, Pm II and Pm IV at lower temperature, whereas Pm I proved to be a more eurytherm species, which nicely correlates with their respective seasonal field distribution pattern in the south-eastern coast of the North Sea and adjacent estuaries. Juvenile development time was also influenced by salinity, with a shorter development time at the lower salinity for all cryptic species. Moreover, Pm III and Pm IV performed better at lower than at the higher salinity. Pm IV also changed its reproductive strategy, depending on the salinity. The effect of salinity was less clearly reflected in the geographical distribution of the four species. Different temperature preferences of the cryptic species on the other hand may result in niche differentiation and can provide an important mechanism for coexistence of these closely related species.

Effects of the oophagous bivalve Acesta oophaga on the morphology and fecundity of its deep‐sea tubeworm host, Lamellibrachia luymesi

AbstractThe deep‐sea bivalve Acesta oophaga lives attached to the anterior end of the vestimentiferan tubeworm, Lamellibrachia luymesi, at cold methane seeps. The bivalve is found almost exclusively on female tubeworms, where it consumes the lipid‐rich eggs of L. luymesi that are spawned year round (Biological Bulletin, 209, 2005, 87). It is apparent that A. oophaga benefits directly from this close association, but the consequences for the tubeworm host may be more complicated than just a simple predator–prey interaction. Since A. oophaga completely surrounds the tube opening and plume of the worm, it is likely that its presence would limit oxygen uptake by L. luymesi, thereby inhibiting worm growth and reproduction. We hypothesized that occupied tubeworms would compensate for this by growing larger plumes for oxygen uptake. To explore the effects of bivalve presence/absence on female tubeworms, several morphological features, including body size, plume length, tube diameter, and tube segment length, as well as instantaneous fecundity, were compared. Results suggest that the mere presence of A. oophaga has a significant impact on the morphology of its host worm, as all measures of worm size, except for tube segment length, were significantly greater with clams present. Additionally, instantaneous fecundity was 3.5 times higher in occupied worms, implying that tubeworms are not oxygen‐deprived or energy limited as a result of bivalve presence. Our findings suggest that the association between these two deep‐sea organisms may be a more complex form of symbiosis than the simple predator–prey relationship, as previously thought.

A paradoxical mismatch of fecundity and recruitment in deep-sea opportunists: Cocculinid and pseudococculinid limpets colonizing vascular plant remains on the Bahamian Slope

Between 1992 and 1994, palm fronds and bundles of fibrous material (rolled door mats of Chinese dragon grass) were deployed by submersible every 3 months at 520m depth in the Tongue of the Ocean, Bahamas. Substrata were recovered after 3-month and 6-month exposure periods and searched intensively for invertebrate colonists. Recruitment surfaces were colonized during every exposure period by three species of cocculiniform limpets, Cocculina rathbuni, Cocculina emsoni, and Notocrater youngi. At least two species appeared in each season, but the relative numbers varied in a way that may indicate seasonal differences in reproduction. Gonad development could be observed through the transparent shell of C. rathbuni, which attained sexual maturity in less than 3 months and had a maximum instantaneous fecundity of 40 eggs. Growth rates (0.025–0.044mm/day) were high when scaled to adult body size. We used current-meter data from the deployment site to calculate the fluxes of larvae that would be required to produce the measured levels of recruitment. Observed recruitment would require larval densities of hundreds of thousands to millions of larvae per km3. Nevertheless, it is remarkable that these snails are able to succeed with an opportunistic strategy given their low fecundity and lecithotrophic development.

Vegetative reproduction in “Heterosiphonia japonica” (Dasyaceae, Ceramiales, Rhodophyta), an introduced red alga on European coasts

Vegetative reproduction by means of abscised fragments was studied in the introduced red alga ‘‘Heterosiphonia japonica’’. Small side branches (pseudolaterals) are actively shed in all seasons, but mostly during late summer/autumn. The development of excised pseudolaterals was studied in the laboratory under different culture conditions. At 08C, few pseudolaterals survived and no development was observed. At 48C, survival was high but development was slow, while at 12 and 208C the majority of pseudolaterals developed rhizoids and attached to the substratum. Aquarium studies of fragmentation rate of pseudolaterals and estimates of tetraspore production showed that the instantaneous fecundity by fragments could be almost as high as the estimated fecundity by tetraspores. Field observations showed recruitment of ‘‘H. japonica’’ by fragments during all seasons. There was a weak trend of higher densities of recruits originating from fragments during late summer, consistent with the high degree of pseudolateral shedding and optimal temperature for pseudolateral development at this time of the year. The results from this study show that the newly introduced species has a high capacity for regenerating from small branchlets, and a continuous release of these vegetative propagules throughout the year.

The life history responses of the abalone pest, Terebrasabella heterouncinata, under natural and aquaculture conditions

The sabellid, Terebrasabella heterouncinata, is a small (<5 mm) intratubular brooder that lives in burrows within the host’s shell matrix. It is a semi-continuous breeder and despite producing small numbers of large eggs, infestation by this animal has reached epidemic proportions on local abalone farms. The present study compared the morphometrics and reproductive characteristics of worms from farmed and wild abalone, in the Walker Bay area of the south Western Cape Province of South Africa, to gain insights into why this animal has become so successful under aquaculture conditions. The farms designated farm A and farm B each had one “on-farm” site, and two wild sites, while farm C had two on-farm sites and two wild sites. The wild sites were natural abalone habitats located within 2.5 km of the farms. Our results conclusively showed that environmental conditions prevalent on the farms enhanced the reproductive success of these worms relative to that observed in its natural environment. At farms B and C, worms occurred in significantly higher densities at the on-farm sites than in the corresponding wild samples, but at farm A, density was equally low at the three sites. At all three farms, a greater proportion of the population was reproductively active in the on-farm samples than in the wild samples. Worms on farmed abalone had a higher instantaneous fecundity, brooded more clutches simultaneously and were larger than their conspecifics from the wild. There was a positive correlation between adult size and brood size and the number of clutches brooded simultaneously. Within the three on-farm sites there was a negative correlation between egg volume and brood size, indicating a trade-off between these traits. However, such a trade-off was not apparent between sites, with brood size being higher at the on-farm sites than at the wild sites, irrespective of egg size. This suggests that the stable nutrient-enriched environment on the farm led to an increase in fecundity without compromising the size (and implicitly the quality) of the eggs. Worm density did not have a significant effect on body size or any other reproductive traits at most sites, and the density of T. heterouncinata was unaffected by the density of other shell-infesting polychaetes. The results suggest that the farm environment has selected for larger, more fecund worms that breed rapidly with high recruitment success as a consequence of abundant nutrients, high host density, habitat stability and a possible lack of predation and interspecific competition.

Reproductive performance of hatchery-bred donkey's ear abalone, Haliotis asinina , Linne, fed natural and artificial diets

Hatchery-bred donkey's ear abalone, Haliotis asinina, Linne broodstock were given diets consisting of natural food, seaweed (SW), Gracilariopsis bailinae, D1; combination of SW and artificial diet (AD), D2; and AD alone, D3. Equal numbers of 1 : 1 female and male abalone were stocked in 24 units, 60 L tanks with eight replicate tanks per dietary treatment. Reproductive performance, e.g. number of spawnings, instantaneous fecundity and egg hatching rates, was monitored over 270 days. The mean number of spawnings was not significantly different among treatments. The mean instantaneous fecundity and percent hatching rates were significantly higher in abalone fed D2 or D3 compared to those given D1. Survival of abalone broodstock fed D1 was, however, significantly higher at 88% than those fed either D2 or D3 at 75%. Fatty acid analysis showed that the n-3/n-6 fatty acid ratios of abalone hepatopancreas reflected those of their diets. Mature abalone ovary had n-3/n-6 fatty acid ratio of 1.3. A higher amount of essential nutrients in the artificial diet such as protein, lipid and the highly unsaturated fatty acids, e.g. 20 : 4n-6, 20 : 5n-3, 22 : 6n-3 in abalone fed D2 or D3, may have influenced the increased reproductive performance.

Reptilian and Avian Ovarian Cycles and the Evolutionary Origin of Volant Birds

The first birds probably evolved from a line of theropod dinosaurs in the late Jurassic or early Cretaceous. The "trees down" theory proposes that avian ancestors were arboreal, whereas the "ground-up" (cursorial) theory suggests that they were terrestrial, and ran and jumped for prey. We present suggestive evidence from reptilian and avian female reproductive biology that supports the arboreal theory, although neontological evidence can never authenticate a paleontological event. The "law of follicular constancy" is an empirical observation that the number of ovulations per female per ovulatory cycle (instantaneous fecundity, or IF) is the same regardless of the amount of ovarian tissue present. In vertebrates with an IF of two or more, surgical removal of one of the paired ovaries (unilateral ovariectomy, or ULO) leads to a doubling of ovulations from the remaining ovary (compensatory ovarian hypertrophy, or COH), this ovary cycling at the same frequency as it did before surgery. In vertebrates that produce one egg alternately from each ovary (an IF of one), however, ULO leads to a form of COH in which the remaining ovary still ovulates one egg at a time but twice as frequently. In most birds, only the left ovary is present; it ovulates a single egg every 1-2 days until the species-specific clutch size is reached. Inasmuch as this avian ovulatory pattern is similar to an accelerated version of that occurring after ULO in a species that alternates ovulation, we propose that birds evolved from dinosaurs with such a pattern. A great majority of extant reptiles with an IF of one are either anoline or gekkonid lizards, and many of these ovulate several times a year. Furthermore, most species in these tropical groups are arboreal. Even considering phylogenetic constraints within anoline and gekkonid lizards, we propose that correlations of arboreality and an IF of one in these groups are implied as adaptive relationships and represent ecological parallelisms. Therefore, we propose that the ancestors of birds were arboreal. Furthermore, they probably were of small size, as are all lizards with an IF of one.

The Comparative Anatomy of Lizard Ovaries, with Emphasis on the Number of Germinal Beds

Germinal bed (GB) number in ovaries of 26 lizard species is described. This infor- mation, along with previous data on 14 other lizards, allowed us to form the following hypotheses concerning the relationships of GB number and (1) the numbers of growing and atretic follicles in the preovulatory ovary, (2) instantaneous fecundity, (3) geographic distribution, and (4) taxonomic relationship. Germinal bed number can vary within a family, but may be consistent within other families and also within genera. The 11 species with one GB per ovary are tropical or subtropical, or are derived from a primarily tropical genus, and exhibit a relatively low instantaneous fecundity (usually 1 egg). In contrast, all but one of the 21 temperate species examined have two GBs per ovary, but some tropical or subtropical species also exhibit this ovarian condition. Presence of two GBs per ovary is related to a wide range of instantaneous fecundities. In these species, rates of follicular atresia in preovulatory ovaries are inversely proportional to instantaneous fecundity. Species with one GB per ovary have not readily evolved new forms with higher instantaneous fecundities in the past. In contrast, the condition of two (or several) GBs per ovary has been asso- ciated with greater phylogenetic flexibility of instantaneous fecundity. In the latter species, evo- lutionary changes in pituitary FSH secretion, which affect both the number of ovarian follicles and rates of follicular atresia, may have mediated changes in instantaneous fecundity. Testing of these hypotheses must await more data on the number of GBs and growing and atretic follicles in pre- ovulatory ovaries of more lizard species.