Are crabeater seals, Lobodon carcinophaga , sexually dimorphic for size during the breeding season?

2018 ◽  
Vol 35 (2) ◽  
pp. 677-683
Author(s):  
Peter D. Shaughnessy ◽  
Colin Southwell
Keyword(s):  
Breeding Season ◽  
Sexually Dimorphic ◽  
Crabeater Seals

scholarly journals Phenotype-limited distributions: short-billed birds move away during times that prey bury deeply

2015 ◽  
Vol 2 (6) ◽  
pp. 150073 ◽  
Author(s):  
Sjoerd Duijns ◽  
Jan A. van Gils ◽  
Jennifer Smart ◽  
Theunis Piersma
Keyword(s):  
Breeding Season ◽  
Resource Use ◽  
Environmental Conditions ◽  
Wadden Sea ◽  
Phenotypic Traits ◽  
Sexually Dimorphic ◽  
Phenotypic Evolution ◽  
Main Prey ◽  
Limited Distribution ◽  
Widespread Phenomenon

In our seasonal world, animals face a variety of environmental conditions in the course of the year. To cope with such seasonality, animals may be phenotypically flexible, but some phenotypic traits are fixed. If fixed phenotypic traits are functionally linked to resource use, then animals should redistribute in response to seasonally changing resources, leading to a ‘phenotype-limited’ distribution. Here, we examine this possibility for a shorebird, the bar-tailed godwit ( Limosa lapponica ; a long-billed and sexually dimorphic shorebird), that has to reach buried prey with a probing bill of fixed length. The main prey of female bar-tailed godwits is buried deeper in winter than in summer. Using sightings of individually marked females, we found that in winter only longer-billed individuals remained in the Dutch Wadden Sea, while the shorter-billed individuals moved away to an estuary with a more benign climate such as the Wash. Although longer-billed individuals have the widest range of options in winter and could therefore be selected for, counterselection may occur during the breeding season on the tundra, where surface-living prey may be captured more easily with shorter bills. Phenotype-limited distributions could be a widespread phenomenon and, when associated with assortative migration and mating, it may act as a precursor of phenotypic evolution.

Estimating mean age at sexual maturity in the crabeater seal (Lobodon carcinophagus)

1995 ◽  
Vol 52 (11) ◽  
pp. 2347-2352 ◽  
Author(s):  
Karin C. Hårding ◽  
Tero Härkönen
Keyword(s):  
Breeding Season ◽  
Sexual Maturity ◽  
Reproductive Status ◽  
Strong Indication ◽  
Specific Population ◽  
Crabeater Seal ◽  
Crabeater Seals ◽  
Lobodon Carcinophagus

Mean age at sexual maturity (ASM) in crabeater seals (Lobodon carcinophagus) was estimated according to two different methods. Samples were from 1964, 1977, and 1989. Using the first method, the estimated ASM in 1989 was 6.57 ± 0.82 years, which was considerably older than reported earlier. This estimate is the only one existing for crabeater seals that can be used to compare populations and species. The first method was based on the maturity rate at age. Behavioural segregation of mature and immature seals could give skewed maturity rates in samples. Because the 1964 and the 1977 samples were collected during a season when segregated behaviour was expected (breeding season), results from these years were not comparable with the 1989 estimate (collected during moult). The second method does not produce absolute values of ASM, but the estimates could be used as indices of ASM within a specific population. There was a statistically significant increase in the ASM index in 1989 (4.93 ± 0.57), compared with 1964 (3.75 ± 0.31) and 1977 (3.80 ± 0.44). This is a strong indication of a true increase in ASM in crabeater seals. Recommendations are made to improve future procedures for studying reproductive status in seals.

The evolution of sexual dimorphism in the skink Eumeces laticeps: an example of sexual selection

1985 ◽  
Vol 63 (5) ◽  
pp. 995-1002 ◽  
Author(s):  
Laurie J. Vitt ◽  
William E. Cooper Jr.
Keyword(s):  
Sexual Selection ◽  
Body Size ◽  
Breeding Season ◽  
Prey Size ◽  
Maximum Size ◽  
Head Size ◽  
Sexually Dimorphic ◽  
Eumeces Laticeps ◽  
Aggressive Male ◽  
The Mean

Adults of the skink Eumeces laticeps are sexually dimorphic in coloration, body size, head size, and relative head size. Males have larger heads at a given body size than females and the divergence in relative head size is coincident with the size at which sexual maturity is reached. Although there were no differences between sexes in tail loss frequencies, there were substantial differences in frequencies of body and head scars, a consequence of aggressive male–male interactions. Prey size was correlated with body and head size and males tended to eat larger prey items than females. However, both sexes are capable of eating prey much larger than the mean or maximum size of prey found in stomachs, suggesting that resource partitioning is a consequence of sexual size differences rather than a cause. The heads of males at a given body size increase during the breeding season, and a combination of head and body size apparently determines the outcome of intrasexual aggressive encounters. Moreover, small males were never observed with females during the breeding season, and those males observed "guarding" females were significantly larger than males observed in the absence of females. We conclude that sexual selection accounts for many of the differences in morphological traits between sexes of E. laticeps.

scholarly journals The reproductive biology of a Central American cichlid Neetroplus nematopus in Lake Xiloá, Nicaragua

2010 ◽  
Vol 56 (1) ◽  
pp. 43-51 ◽  
Author(s):  
Kenneth R. McKaye ◽  
Jeremy Hale ◽  
Eric P. van den Berghe
Keyword(s):  
Survival Rate ◽  
Breeding Season ◽  
Cichlid Fish ◽  
Central American ◽  
Stabilizing Selection ◽  
Sexually Dimorphic ◽  
Male Body ◽  
Overall Survival Rate ◽  
Breeding Sites ◽  
Fishing Practices

Abstract This study was conducted to provide a five-year database on the breeding seasonality and breeding biology of a Central American cichlid fish Neetroplus nematopus, a biparental substratum-spawning cichlid that cares for its eggs, wrigglers, and fry for up to six weeks. A total of 503 breeding pairs were monitored for breeding success. Breeding pairs of N. nematopus are sexually dimorphic in size, with females averaging 39% of male body mass. Fry emerged from 85% of nesting cavities. After three weeks, only 30% of the broods were present in the nesting cavity; these broods had a 30% survival rate, giving a 9% overall survival rate. Nineteen percent of the successful parents with three-week-old broods adopted foreign fry. A consistent unimodal breeding peak in December was observed for five years. This breeding peak differed dramatically from the bimodal breeding season 20 years found in the 1970s. The effects of extensive grenade fishing practices during the 1980s might have played a substantial role in the observed change. Grenade fishing stopped in 1991, and the number of N. nematopus pairs increased by 136% from 1990 to 1995. With increased density of breeding fish, the breeding season for this species also expanded. The balance between divergent selection due to competition for breeding sites and stabilizing selection due to predation pressure on offspring is likely to mold the breeding season for N. nematopus and other cichlids of Lake Xiloá. We suggest that brood adoption and synchrony of breeding is a strategy to reduce predation on the parent's own young.

Sexually dimorphic spatial learning in meadow voles Microtus pennsylvanicus and deer mice Peromyscus maniculatus.

1996 ◽  
Vol 199 (1) ◽  
pp. 195-200 ◽  
Author(s):  
L A Galea ◽  
M Kavaliers ◽  
K P Ossenkopp
Keyword(s):  
Breeding Season ◽  
Spatial Learning ◽  
Water Maze ◽  
Microtus Pennsylvanicus ◽  
Group Differences ◽  
Deer Mice ◽  
Sexually Dimorphic ◽  
Meadow Voles ◽  
Spatial Performance ◽  
Males And Females

A number of studies examining developmental, neural and hormonal aspects of sexually dimorphic spatial learning (Morris water-maze) in meadow voles (Microtus pennsylvanicus) and deer mice (Peromyscus maniculatus) are described. We found that, in adult deer mice, female spatial performance decreased during the breeding season relative to the non-breeding season, whereas the reverse pattern was observed in male performance. There was a sex difference favouring males in spatial learning during the breeding season, but not during the non-breeding season. In adult meadow voles, females with low levels of oestradiol and males performed better in the water-maze than females with high levels of oestradiol. Postweaning voles (20 and 25 days after birth) acquired the water-maze task more quickly than preweaning voles (day 10). No sex difference in water-maze performance was evident at any of these juvenile ages. When these same voles were tested again as adults to investigate retention and re-acquisition of the water-maze, both males and females from male-biased litters re-acquired the task better than males and females from female-biased litters. Together, the results of these studies indicate that sexually dimorphic spatial ability is dependent on the organization (in utero) and activational effects of gonadal hormones. These studies provide the first demonstration of the influence of natural changes in reproductive status on spatial learning of deer mice and meadow voles. The results also demonstrate that spatial performance of males and females is differentially affected by changes in reproductive status and that group differences in the laboratory are associated with group differences in space utilization in the wild. These findings help to clarify previous apparently contradictory findings about sex differences in spatial ability.

Reproductive Behaviour and Early Development of the Empire Fish Hypseleotris compressus (Eleotridae)

1978 ◽  
Vol 29 (5) ◽  
pp. 585 ◽  
Author(s):  
EH Auty
Keyword(s):  
Early Development ◽  
Breeding Season ◽  
Alimentary Tract ◽  
Reproductive Behaviour ◽  
Sexually Dimorphic ◽  
Australian Freshwater ◽  
Courtship Displays

H. compressus is a small Australian freshwater eleotrid which is sexually dimorphic. The colourful male is involved in aggressive and courtship displays throughout a protracted breeding season and also guards the eggs during their short development. The female is capable of spawning repeatedly throughout the breeding season and it is estimated that she may produce at least 40000 eggs per season. The eggs are very small, being approximately 0.32 mm on the longest axis, and are transparent and adhesive. Hatching usually occurs between 10 and 14 h after fertilization. The newly hatched prolarvae are poorly developed, without rayed fins or an alimentary tract. Their development was observed for 10 days by which time the yolk had been lost but no larvae survived beyond this point.

reproductive biology of centrophorus cf. uyato from the cayman trench, jamaica

2005 ◽  
Vol 85 (5) ◽  
pp. 1185-1192 ◽  
Author(s):  
donna m. mclaughlin ◽  
john f. morrissey
Keyword(s):  
Reproductive Biology ◽  
Breeding Season ◽  
Mature Female ◽  
Sexual Segregation ◽  
Mature Male ◽  
Sexually Dimorphic ◽  
Total Length ◽  
Over Exploitation

the taxonomy of the genus centrophorus (squaliformes: squalidae) is currently in a great deal of uncertainty. the characteristics of the species subject to the present study most closely resemble those of centrophorus uyato, hence the use of centrophorus cf. uyato, though the species in question may be a species of centrophorus that has not been described previously. specimens were obtained via vertical and horizontal longline at depths of 250–913 m. the reproductive biology of 51 female and 8 male centrophorus cf. uyato were examined. this species is sexually dimorphic, with females attaining a larger size than males. the smallest mature male was 81.2 cm total length whereas the smallest mature female was 91.5 cm total length. females are aplacentally viviparous, with the pups acquiring nutrition via large external yolk sacs, and there was a maximum of two pups per litter. oocytes continued to develop throughout gestation. most females carrying developing embryos had two large (>3.3 cm), equally developed ovarian oocytes, which leads us to believe that they ovulate soon after parturition. this species seems to exhibit complete sexual segregation during the non-breeding season, with mature males absent from the study site during summer months. centrophorus cf. uyato may have one of the lowest fecundities among sharks, giving birth to a maximum of two pups every three years. all species in genus centrophorus have small litters (<6) making them vulnerable to over-exploitation.

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