Variation In Reproductive Potential Research Articles

Diversity, divergence and density: How habitat and hybrid zone dynamics maintain a genomic cline in an intertidal barnacle

AbstractAimAs within‐species genomic data have been shown useful in interpreting broader biogeographic trends, we analysed the mode of population genomic isolation involved in a well‐studied intertidal genomic cline to better understand the mechanisms maintaining it. These results were interpreted in the context of spatial variation in habitat use and availability as well as likely fitness consequences for hybridization between the two lineages.LocationPacific coast of North America.TaxonArthropods (Class Maxillopoda, Order Sessilia, Family Balanidae;Balanus glandula).MethodsGenotype‐by‐sequencing approaches were used to generate single‐nucleotide polymorphism markers across sites sampled between southern Alaska and Southern California. Inference using standard population genomic methods, including analysis of population structure, inbreeding and linkage disequilibrium, was used to identify the steepest transitions across the largest number of loci examined. These data were put in the context of observed population density and habitat availability.ResultsWe show that the majority of markers analysed show strong clinal transitions in a very narrow portion of the California coast. Patterns of linkage disequilibrium among markers, along with prior evidence of variation in reproductive potential by latitude and by mitochondrial lineage, suggest some reproductive isolation among the northern and southern lineages ofB. glandulathat are concordant with the drop in population density and habitat availability in central California.Main ConclusionsA significant clinal transition in genomic diversity is stronger and more localized than previously recognized and exhibits statistical patterns suggesting that the lineages are reproductively and phenotypically distinct in ways that may be ecologically important. As this species has been used to infer process in coastal biogeography, further study of concordant patterns will be important for advancing our understanding of this region.

Age-related variation in reproductive potential and influence on recruitment of western sand lance Ammodytes japonicus in the Seto Inland Sea, western Japan

Assessment of total egg production as a proxy for reproductive potential is critical for understanding the mechanisms of recruitment variability and implementing appropriate stock management. This study determined whether the temporal variation in the estimated egg production index (EPI) of spawning western sand lance (Ammodytes japonicus) collected in the Bisan Strait in the central Seto Inland Sea in Japan explains its recruitment variability from 2009 to 2019. Although the maturation rates of individuals aged 1 year varied among sampling years, they were positively correlated with mean standard length at aestivation onset in summer. The negative relationship between the mean standard length and density of aestivating young-of-the-year fish at aestivation onset suggests that growth was dependent on density during the spring foraging period. All specimens aged 2 and 3 years were mature, and relative fecundity was significantly higher than that in specimens aged 1 year. The EPI of spawning individuals was markedly reduced in recent years and was associated with the decreased density of fish aged 2 and 3 years. In addition, the number of recruit fish was significantly associated with the EPI of spawning fish. However, the density of spawning fish in winter did not adequately explain the variation in recruitment. Thus, our findings suggest that sand lance aged 1 year have reduced reproductive potential, and that the causes of the recent decline in sand lance stocks might be partly attributable to a decline in the abundance of older fish.

Variations in reproductive potential between nearshore and offshore spawning contingents of hogfish in the eastern Gulf of Mexico

Hogfish, Lachnolaimus maximus (Walbaum), have multiple traits that confound measuring reproductive potential: they are protogynous, relatively long-lived harem-forming fish that spawn daily for months. Additionally, recent evidence demonstrates that size, age and timing of sex change vary on a spatial scale within the study area (West Florida shelf, USA). This study investigates the effect of this spatial variation on hogfish reproductive potential by evaluating spawning seasonality, spawning frequency and batch fecundity using an indeterminate egg production model. Offshore females were larger than nearshore females, and batch fecundity was related in a log-linear manner to female size. Gonad histology demonstrated a more protracted reproductive period for females offshore (8 months) than nearshore (4 months). Spatial variations in size coincide with ontogeny because hogfish move offshore with growth; however, even after accounting for fish size, offshore females spawned more. In areas where male removal rates are elevated, spawning harems are disrupted; thus, greater fishing effort nearshore may further reduce the reproductive potential of these females. These nearshore and offshore spawning components of the population are not genetically distinct, but instead represent two contingent spawning strategies that likely enhance total population stability and resilience of this stock in the eastern Gulf of Mexico.

A unique nest-protection strategy in a new species of spider wasp.

Hymenoptera show a great variation in reproductive potential and nesting behavior, from thousands of eggs in sawflies to just a dozen in nest-provisioning wasps. Reduction in reproductive potential in evolutionary derived Hymenoptera is often facilitated by advanced behavioral mechanisms and nesting strategies. Here we describe a surprising nesting behavior that was previously unknown in the entire animal kingdom: the use of a vestibular cell filled with dead ants in a new spider wasp (Hymenoptera: Pompilidae) species collected with trap nests in South-East China. We scientifically describe the ‘Bone-house Wasp’ as Deuteragenia ossarium sp. nov., named after graveyard bone-houses or ossuaries. We show that D. ossarium nests are less vulnerable to natural enemies than nests of other sympatric trap-nesting wasps, suggesting an effective nest protection strategy, most likely by utilizing chemical cues emanating from the dead ants.

Intraspecific variation in reproductive potential with maternal body size in Gulf killifish Fundulus grandis

Gulf killifish Fundulus grandis show promise for commercial development as a baitfish species marketed to anglers on the U.S. Gulf Coast. Additionally, fishes in the genus Fundulus are increasingly cultured as model organisms for various fields of scientific inquiry. Research examining effects of maternal body size on reproduction in this genus and more generally in fractional spawning species with eggs capable of terrestrial development is lacking. The present study assessed the effects of female body size on reproductive investment in laboratory held Gulf killifish as well as subsequent implications for larvae. Larger females had significantly higher fecundity and produced individual eggs of greater volume. Gonadosomatic index more than doubled as female body mass increased from 6.9 to 12.9g, but did not increase significantly in females of body mass>12.9g. Larger eggs required significantly longer incubation periods, and newly hatched larvae from larger eggs had more endogenous nutritional resources but shorter body length. Experimental results describe maternal effects in a fractional spawning species producing eggs with the ability to incubate terrestrially. Results also provide practically useful information for aquaculturists as F. grandis are increasingly cultured commercially and in laboratory settings.

Experimentally induced variation in the physical reproductive potential and mating success in honey bee queens

In honeybee colonies, reproduction is monopolized by the queen while her daughter workers are facultatively sterile. Caste determination is a consequence of environmental conditions during development, during which female larvae may become either queens or workers depending on their larval diet. This bipotency introduces significant variation in the reproductive potential of queen bees, with queens raised from young worker larvae exhibiting high reproductive potential and queens raised from older worker larvae exhibiting lower reproductive potential. We verify that low-quality queens are indeed produced from older worker larvae, as measured morphometrically (e.g., body size) and by stored sperm counts. We also show, for the first time, that low-quality queens mate with significantly fewer males, which significantly influences the resultant intracolony genetic diversity of the worker force of their future colonies. These results demonstrate a reproductive continuum of honeybee queens and provide insights into the reproductive constraints of social insects.

Effects of Maternal Growth on Fecundity and Egg Quality of Wild and Captive Atka Mackerel

AbstractTrade‐offs in energy allocation between growth and reproduction can result in variations in reproductive potential in fish with differing growth patterns. Spawning biomass is often used as a proxy for reproductive potential on the assumption that fecundity is directly proportional to body weight. We examined variations in the reproductive potential of Atka mackerel Pleurogrammus monopterygius by studying the effect of differential growth and condition patterns on fecundity, atresia, and egg energy. Fecundity and egg energy were determined for fish from two geographic areas, Seguam Pass and Amchitka Island, Alaska, and compared with those of fish held in captivity. These Atka mackerel showed distinct differences in growth and condition, with weight at length and length at age being the highest among captive fish, intermediate among fish from Seguam Pass, and lowest among fish from Amchitka Island. Realized fecundity showed that on average captive fish spawned seven batches, fish from Seguam Pass six batches, and fish from Amchitka Island five batches. For wild fish, potential and realized fecundity at length or age was significantly higher at Seguam Pass than at Amchitka Island, whereas the fecundity‐at‐weight relationship did not differ by area, suggesting that weight is a better predictor of fecundity than length or age. Atresia and batch fecundity by length or weight did not differ by area, suggesting that the variation in fecundity is better explained by the variation in batch number than by batch size. Oocyte dry weight was higher for captive fish than for wild fish, whereas batch order did not significantly affect oocyte dry weight. Increased potential fecundity, realized fecundity, and oocyte quality in Atka mackerel females were strongly related to body size, indicating that growth differences and maternal feeding success impact the fecundity and oocyte quality of Atka mackerel. Therefore, changes in growth and condition patterns need to be taken into account to accurately estimate the reproductive potential of this species.Received August 21, 2010; accepted March 2, 2011

Variation in reproductive potential and influence on Icelandic herring recruitment

Explaining recruitment variation in fish is essential for successful fishery management and is consequently under constant review, with an increasing focus on how maternal factors, relative to environmental influences, operate at the level of individual female spawners and extend from the spawning stock through to recruitment. We estimate total egg production (E) in Icelandic summer-spawning herring (Clupea harengus) from 1963 through 1999 by using sequential population analyses (SPA) and their estimates of stock biomass and recruitment, various size and maturity metrics, and individual fecundity estimates that rely on total length and the condition of the spawners. Generalized linear models indicate that maternal effects are of significance in explaining SPA-based recruitment-at-age-3 (R). The best model explained 64% of the variation in R and incorporates E constrained to the repeat spawners (40%), the NAO winter index (18%) and ocean temperature (6%). The latter two represent the winter and spring periods subsequent to year-class formation. Recruit spawner contributions to E were of no significance in explaining variation in R despite the fact that they could contribute as much as 55% of E when their contribution to E was consistently underestimated by a factor of � 2, based only on their contribution to spawning stock biomass. We conclude that the spawning potential of the repeat spawners should replace total spawning stock biomass for determining recruitment potential in stock assessment. In addition to the incorporation of oceanographic factors, this

Seasonal cycles in population abundances and egg production rates in the planktonic copepods Centropages typicus and Acartia clausi

Laboratory studies on the seasonal cycling of egg production rates for Centropages typicus and Acartia clausi did not reflect seasonal changes in densities for these species at sea. Maximum egg production rates occurred from autumn to spring when population abundances at sea were low. In late spring, an increment in population numbers was followed by a drastic decline in egg deposition which continued into summer. The percentage loss due to mortality, calculated using egg data and total number of copepodid stages CIII and CIV recorded at sea ˜2 weeks later, indicated greatest mortality (80–99%) from eggs to copepodids during periods of high breeding intensity. These results suggest that high and low density phases in population numbers may be the outcome of variations in reproductive potential and survival rates of eggs and immature stages rather than reproductive potential per se .

Reproduction of annual eelgrass: Variation among habitats and comparison with perennial eelgrass ( Zostera marina L.)

The variation in reproductive potential of annual eelgrass was examined along a continuous gradient on an extensive mudflat bordering on and sloping down from the shore (Eastern River) and in a habitat mosaic in a salt marsh (Petpeswick Inlet) in Nova Scotia. Spathe and flower production as well as plant density were compared among habitats. Of the four habitats investigated in Petpeswick Inlet, the largest numbers of spathes and flowers per spathe were produced by plants in ponds on raised flats of Spartina alterniflora Loisel. The highest number of seeds per unit area was produced by plants in depressions on these flats which drained with each low tide. Seed production of annual eelgrass in drained depressions (4 889 seeds per 625 cm 2) was seven times that of perennial shoots in creeks and higher than any records in the literature for perennial eelgrass. On average, seed production of annual eelgrass in this study was higher than values reported for other locations. Along the gradient, both annual and perennial eelgrass showed peaks in reproductive potential, but the annual peaked further up the gradient where there was greater exposure to air at low tide. Transplanting studies indicated that the among-habitat differences in reproductive potential were largely controlled by environmental as opposed to genetic factors. The possible effect of inter- and intraspecific competition on the reproductive potential of annual eelgrass was investigated experimentally in two habitats where co-existing species were abundant. In creeks the presence of perennial eelgrass significantly reduced the reproductive potential of annual eelgrass, but in a drained depression, the removal of Ruppia maritima L. s.l. had no effect. The upper distribution limit of annual eelgrass is likely determined by desiccation while the lower limit is probably determined by a combination of light availability (to some extent affected by perennial eelgrass) and exposure to spring rains which would significantly enhance seed germination.

Ecology and conservation of an endangered rattlesnake, Sistrurus catenatus, in Missouri, USA

The life history and ecology of the massasauga Sistrurus catenatus, an endangered rattlesnake, was studied from 1979 to 1983 at the Squaw Creek National Wildlife Refuge, Missouri, USA. Except for tail length, this population exhibits little sexual dimorphism. Massasaugas are active from April to October, and are primarily diurnal, except in summer. Snakes are found mainly in a cordgrass prairie in spring and autumn, utilising drier, upland areas in summer. Mean brood size for this population was 6·35, and there was a significant positive relationship between brood size and female body size. Although this species apparently demonstrates considerable geographic variation in reproductive potential, the significance of this variation cannot be currently assessed. Growth rates, estimated from size-frequency data, suggest an age of maturity of 3–4 years for females. Massasaugas at Squaw Creek feed mainly on rodents and other snakes. Current refuge practices, such as controlled burning of the prairie and unrestricted visitor usage, may have significant negative impacts on Sistrurus populations. Recommendations for mitigating these impacts are provided.

The origin of helping: The role of variability in reproductive potential

We investigate the relationship between variation in reproductive potential among members of a family and genetic relatedness to determine which combinations favor natural selection for helping behavior. Conditions favoring helping are derived for the helper, the recipient, and the parents of these individuals. Our analysis reveals that a factor of general significance in the evolution of social organisms is variability in reproductive potential among offspring of a parent. To a limited extent this factor has already been appreciated because of its implicit role in "facultative altruism" and "parental manipulation", or suppression of offspring or sibs; however, the unifying role of variance per se and the ways by which it may act have not been widely appreciated. We show that suppression as a source of intra-brood variance is less powerful in the evolution of sociality than other, natural, sources of variance. The facts of natural history appear to be more consistent with a model utilizing natural variance than with a variance-enhancement model for most vertebrates. We present models for discrete and for overlapping generations. Fecundity of young potential helpers relative to adults is an important source of variance for the origin of helping.

Reproductive Cycles In Diaptomid Copepods: Effects of Temperature, Photocycle, and Species on Reproductive Potential

Periodic changes in the oviducts of Diaptomus characterize a reproductive cycle in which females oscillate between gravid and nongravid conditions. The duration of the nongravid condition sets an upper limit for rates of clutch production. In laboratory studies of Diaptomus leptopus, D. pygmaeus, D. pallidus, and D. dorsalis, the cycle was unaffected by photoperiod but showed a strong temperature dependency. At a given temperature, the four species had a common cycle period but spent different amounts of time in the two phases of the cycle. Interspecific differences in the duration of the nongravid phase produced substantial variation in reproductive potential.

Seasonal Variation in Reproductive Potential: A Programmed Feature of Aphid Life Cycles

SUMMARY (1) Individuals of six species of aphid from two families were dissected and the number of ovarioles recorded. Variation in ovariole number occurred within and between generations. The spring generation(s) in each species had the highest number. (2) Generations with many ovarioles were more fecund than those with few. In those generations showing variability an individual with a high number of ovarioles was potentially more fecund and reproduced at a greater rate than individuals with few ovarioles. (3) The changes in reproductive potential are programmed and anticipate predictable