Long-term survival, length of breeding season, and operational sex ratio in a boreal population of common frogs, Rana temporaria L.

1990 ◽  
Vol 68 (1) ◽  
pp. 121-127 ◽  
Author(s):  
Johan Elmberg
Keyword(s):  
Sex Ratio ◽  
Breeding Season ◽  
Rana Temporaria ◽  
Return Rate ◽  
Operational Sex Ratio ◽  
Adult Males ◽  
Term Survival ◽  
Size Dependent ◽  
Survival Selection

A population of individually marked adult Rana temporaria was studied during the breeding season in 1979–1988 in east-central Sweden. Annual return rate averaged 31% (range 16–51%) in males and 16% (range 5–33%) in females. Return rate was not size dependent but increased with every successful previous hibernation, indicating an increased survival rate with age. Return rate was not correlated with winter harshness. Once adult, males had on average 1.5 (maximum 6) seasons with the possibility of reproducing. Corresponding values for females were 1.4 and 4. Mean length of the breeding season was 20 (SD = 2) days. Calling generally started at water temperatures below 3 °C. The lowest spawning temperature was 1 °C. Average temperatures at spawning onset and peak spawning were 5 and 6 °C, respectively. Large males tended to arrive earlier at the pond than small males. Males arrived earlier and stayed longer than did females. The overall population sex ratio was close to unity. The operational sex ratio (OSR) varied during the breeding season, averaging 0.54 (one female to two males). No male was observed to mate more than once per season. I argue that survival selection is more important to male lifetime mating success than is competition in the breeding pond (sexual selection as affected by OSR and length of the breeding season).

Facultative sex allocation in the viviparous lizard Eulamprus tympanum, a species with temperature-dependent sex determination

2003 ◽  
Vol 51 (4) ◽  
pp. 367 ◽  
Author(s):  
Kylie A. Robert ◽  
Michael B. Thompson ◽  
Frank Seebacher
Keyword(s):  
Sex Ratio ◽  
Sex Determination ◽  
Breeding Season ◽  
Sex Allocation ◽  
Adult Population ◽  
Selective Advantage ◽  
Adult Males ◽  
Temperature Dependent ◽  
Maternal Manipulation

Females of the Australian scincid lizard Eulamprus tympanum can manipulate the sex of their offspring in response to gender imbalances in the population using temperature-dependent sex determination. Here we show that when adult males are scarce females produced male-biased litters and when adult males were common females produced female-biased litters. The cues used by a female to assess the adult population are not known but presumably depend upon her experience throughout the breeding season. Maternal manipulation of the sex ratio of the offspring in E. tympanum illustrates a selective advantage of temperature-dependent sex determination in a viviparous species.

scholarly journals Sex ratio and morphological characteristics of rufous gnateaters, Conopophaga lineata (Aves, Passeriformes) in Atlantic forest fragments

2009 ◽  
Vol 99 (1) ◽  
pp. 115-119 ◽  
Author(s):  
Gisele P. M. Dantas ◽  
Fabrício R. Santos ◽  
Miguel Ângelo Marini
Keyword(s):  
Sex Ratio ◽  
Morphological Changes ◽  
Anthropogenic Activities ◽  
Natural Populations ◽  
Morphological Characteristics ◽  
Atlantic Rain Forest ◽  
Forest Fragments ◽  
Natural Habitats ◽  
Term Survival

Unequal sex ratios lead to the loss of genetic variability, decreasing the viability of populations in the long term. Anthropogenic activities often disturb the natural habitats and can cause alterations in sex ratio and morphological characteristics of several species. Forest fragmentation is a major conservation concern, so that understanding its effects in natural populations is essential. In this study, we evaluated the sex ratio and the morphological characteristics of Rufous Gnateaters (Conopophaga lineata (Wied, 1831)) in small and large forest fragments in Minas Gerais, Brazil. Birds (n = 89) were sexed by plumage characteristics and molecular markers. The molecular analysis showed that plumage is not a totally reliable method for sexing Rufous Gnateaters. We observed that sex ratio did not differ between large and small forest fragments, but birds in small fragments had larger wings and tarsus. Wing and tarsus changes may affect the movement ability of individuals within and among forest fragments. In conclusion, Rufous Gnateaters have been able to survive in both small and large Atlantic rain forest fragments without altering their sex ratio, but morphological changes can be prejudicial to their long term survival.

Mating Tactics in the Tropical Millipede Alloporus Uncinatus (Diplopoda: Spirostreptidae)

Behaviour ◽  
1993 ◽  
Vol 124 (1-2) ◽  
pp. 45-56 ◽  
Author(s):  
Steven R. Telford ◽  
J. Mark Dangerfield
Keyword(s):  
Sex Ratio ◽  
Mating System ◽  
Sperm Competition ◽  
Breeding Season ◽  
Female Choice ◽  
Laboratory Experiments ◽  
Mating Behaviour ◽  
Operational Sex Ratio ◽  
Mating Tactics ◽  
Mate Acquisition

AbstractField and laboratory observations of mating behaviour in a population of the tropical millipede Alloporus uncinatus were carried out over one breeding season. Males obtained mates through random encounters and by forming triplet associations with copula pairs. The occurrence of triplet associations in the field was coincident with a highly male biased operational sex ratio. Mate acquisition by males was apparently stochastic and direct physical competition did not occur. In laboratory experiments mating was size-selective probably as a consequence of female choice. We consider the possibility that sperm competition has contributed to the evolution of the mating system in this species.

Large-scale spatiotemporal variation in calf sex ratio in moose (Alces alces): an effect of density-dependent decrease in maternal condition?

2009 ◽  
Vol 87 (4) ◽  
pp. 346-355 ◽  
Author(s):  
K. Bjørneraas ◽  
E. J. Solberg ◽  
I. Herfindal ◽  
B.-E. Sæther
Keyword(s):  
Sex Ratio ◽  
Large Scale ◽  
Alces Alces ◽  
Recruitment Rate ◽  
Spatiotemporal Variation ◽  
Adult Males ◽  
Maternal Condition ◽  
Density Dependent ◽  
Postnatal Mortality

The harvest of Norwegian moose ( Alces alces (L., 1758)) is directed towards certain sex and age classes to maximize yield in terms of meat or number of animals. Observed side effects are declining numbers of calves per female and proportions of adult males, which may affect other demographic variables. Using long-term data, we examined whether spatiotemporal variation in the calf sex ratio was related to changes in (i) density of harvested moose, (ii) recruitment rate, and (or) (iii) the composition of the adult segment of the population. We found declining proportions of male calves in the autumn harvest over time associated with decreasing recruitment rates. Similarly, the proportion of male calves was lower when density of harvested moose was high. We suggest that the decrease in proportion of male calves was caused by increased prenatal or postnatal mortality rates of males, possibly owing to a density-dependent decline in maternal body condition. Proportion of male calves increased with the proportion of adult males in the population the previous year, indicating that low proportions of adult males may lead to lower male recruitment, particularly at high densities. Further declines in proportions of male calves recruited may be avoided by reducing the population density and changing the demographic composition of the harvest.

Does testosterone or coloration affect growth rates of adult males of the lizard Psammodromus algirus?

2000 ◽  
Vol 78 (8) ◽  
pp. 1463-1467 ◽  
Author(s):  
Alfredo Salvador ◽  
José P Veiga
Keyword(s):  
Body Mass ◽  
Breeding Season ◽  
Mass Gain ◽  
Reproductive Period ◽  
The Body ◽  
Adult Males ◽  
Psammodromus Algirus ◽  
Ornamental Traits ◽  
Breeding Coloration

Elevation of circulating testosterone levels during the breeding season stimulates the development of breeding coloration and favors traits that maximize reproductive success, but it may have several costs. Retardation of growth by testosterone has been proposed as one of these costs to males of long-lived species. We examine the results of a field experiment on the short-term (within the breeding season) and long-term (1 year) effects of heightening levels of testosterone on the growth of males of the lacertid lizard Psammodromus algirus. Testosterone did not affect the mass gain of males during the reproductive period or between years. The between-years increase in snout-vent length in testosterone-supplemented males tended to be less than in control individuals. Within-season individual mass gain was mainly determined by body mass at emergence: the lower the body mass the higher the mass gain. Our results do not support the idea that the production of ornamental traits limits growth, as the negative correlation between degree of head coloration and mass gain disappeared when body mass was controlled for.

On the mating system of polar bears

1986 ◽  
Vol 64 (10) ◽  
pp. 2142-2151 ◽  
Author(s):  
Malcolm A. Ramsay ◽  
Ian Stirling
Keyword(s):  
Sex Ratio ◽  
Sea Ice ◽  
Mating System ◽  
Breeding Season ◽  
Large Body ◽  
Arctic Sea Ice ◽  
Polar Bears ◽  
Adult Males ◽  
Terrestrial Mammals ◽  
Adult Females

Polar bears are intimately associated with arctic sea ice and their distribution is approximated by its winter extent. They are the only terrestrial mammals, other than humans, to have adapted so completely to sea ice, a quite different habitat, spatially and temporally, from that occupied by other terrestrial mammals. We propose that the dynamics of sea ice and the associated variability in access to food have played a major role in the evolution of the social structure and mating system of polar bears. Adult females and males move to areas of the sea ice where the greatest success in hunting is realized. Such regions are unpredictable in location, however, both seasonally and annually. Because female distributions are unpredictable, adult males are unable to defend stable territories that will encompass the home ranges of one or more females and may instead distribute themselves among different sea-ice habitats at the same relative densities as solitary adult females. Females keep nursing cubs with them for more than 1 year; hence the mean interbirth interval is 2 or more years. This results in a functionally skewed sex ratio, with fewer females available to breed in any one year than males, and in intrasexual competition among males for access to breeding females. Consequently, established dominance hierarchies among males are unstable, and wounding, scarring, and breakage of canine teeth are common; these are evidence of direct physical confrontations during the breeding season. Large body size is advantageous in these fights and this has resulted in one of the highest degrees of sexual dimorphism among terrestrial mammals. Because of the funtionally skewed sex ratio and the shifting distribution of both females and males, however, even the largest male probably cannot be certain of locating a larger than average number of receptive females in any one breeding season.

Biology of Tiger Sharks (Galeocerdo cuvier) caught by the Queensland Shark Meshing Program off Townsville, Australia

1992 ◽  
Vol 43 (1) ◽  
pp. 33 ◽  
Author(s):  
C Simpfendorfer
Keyword(s):  
Sex Ratio ◽  
Population Size ◽  
Adult Males ◽  
Gill Nets ◽  
Galeocerdo Cuvier ◽  
Total Length ◽  
Sea Snakes ◽  
Apparent Decrease ◽  
Size At Birth

The biology of 835 specimens of Galeocerdo cuvier caught between 1964 and 1986 off Townsville, Australia, was examined. The sharks were caught in a protective meshing programme using both large mesh gill-nets and set lines. The size at birth was estimated to be 80-90 cm total length, and females matured at approximately 287 cm total length. Litter sizes ranged from 6 to 56. Breeding and pupping both appear to occur in summer, with females not breeding every year. Mature females possibly migrate inshore during late spring and summer to give birth. The sex ratio of juveniles and adults favoured females, with few adult males being caught. Ontogenic changes in the diet were observed, with juveniles feeding predominantly on teleosts, sea snakes and birds and adults mostly consuming teleosts, sea snakes, turtles and crabs. There was no apparent decrease in the population size of G. cuvier in the Townsville area as a result of the long-term catching of sharks by the protective meshing programme.

scholarly journals Demography of the enigmatic low phase in a cyclic lemming population

2021 ◽  
Author(s):  
Dominique Fauteux ◽  
Gilles Gauthier
Keyword(s):  
Sex Ratio ◽  
Reproductive Potential ◽  
Indirect Evidence ◽  
Adult Males ◽  
Density Dependent ◽  
Live Trapping ◽  
Biased Sex Ratio ◽  
Males And Females ◽  
Cyclic Populations

Abstract Deciphering the mechanism behind the lack of growth during the prolonged low abundance phase of cyclic populations represents a major challenge due to the lack of data. However, long-term capture-mark-recapture datasets can help resolve this question through demographic analyses. We analysed the demography and movements of cyclic brown lemmings on Bylot Island, Canada, with a 16-yr (2004-2019) live-trapping program and looked for inversely density-dependent factors that could contribute to a prolonged low phase. We found that the proportion of females in the population was inversely density-dependent with a strong male-biased sex ratio at low densities but not at high densities. In contrast, survival of adult females was higher than adult males, but both had lower survival at low densities than at high ones. Distances moved by both adult males and females were density-dependent, and proportion of females in reproductive condition was weakly density-dependent. Individual body condition, measured as monthly change in body mass, was not density-dependent. Overall, the strong malebiased sex ratio at very low densities suggests a loss of reproductive potential due to the rarity of females and appears to be the most susceptible demographic factor that could contribute to the prolonged low phase in cyclic brown lemmings. What leads to this sexbias in the first place is still unclear, but indirect evidence suggests that this may be due to a higher vulnerability of nesting females to predation in winter than males.

Structure and dynamics of a rainforest frog (Litoria genimaculata) population in northern Queensland

2005 ◽  
Vol 53 (4) ◽  
pp. 229 ◽  
Author(s):  
Stephen J. Richards ◽  
Ross A. Alford
Keyword(s):  
Sex Ratio ◽  
Fat Body ◽  
Sympatric Species ◽  
Operational Sex Ratio ◽  
Population Estimates ◽  
Adult Males ◽  
Reproductive Condition ◽  
Structure And Dynamics ◽  
The Mean ◽  
Gravid Females

We studied a population of the rainforest frog Litoria genimaculata over a 7-year period at Birthday Creek, an upland rainforest stream in northern Queensland. Estimated population size on a 60-m transect fluctuated seasonally, decreasing to zero during most winters and reaching a maximum of over 130 during most warmer spring and summer months with an influx of young adult males. Summer population estimates were much smaller during 1990–93, coinciding with the disappearance of two sympatric species. However the L. genimaculata population subsequently recovered to pre-‘decline’ levels. Females were rarely captured along the stream so the operational sex ratio of adult frogs was strongly biased in favour of males (overall sex ratio 1 : 0.04). Sexual dimorphism in this species is extreme. The mean weight of gravid females (23.35 g) was nearly five times that of males (4.68 g) and the ratio of female SVL to male SVL was 1.65. Reproductive and fat-body condition changed seasonally, with males reaching peak reproductive condition in late spring and summer when population densities were greatest. Our data suggest that Litoria genimaculata uses Birthday Creek largely or exclusively as a reproductive habitat. The extent to which this species uses habitats away from stream environments remains to be determined.

The effect of sex ratio on size-assortative mating in two explosively breeding anurans

2015 ◽  
Vol 36 (2) ◽  
pp. 149-154 ◽  
Author(s):  
Jiří Vojar ◽  
Petr Chajma ◽  
Oldřich Kopecký ◽  
Vladimír Puš ◽  
Miroslav Šálek
Keyword(s):  
Sex Ratio ◽  
Assortative Mating ◽  
Rana Temporaria ◽  
Bufo Bufo ◽  
The Body ◽  
Operational Sex Ratio ◽  
Wild Populations ◽  
Individual Fitness ◽  
Widespread Phenomenon ◽  
Males And Females

Size-assortative mating (SAM) is a widespread phenomenon related to individual fitness. In our study, we examined: (i) the appearance of SAM, and (ii) the effect of sex ratio on intensity of SAM in wild populations of two explosively breeding anurans, common frogs,Rana temporaria, and common toads,Bufo bufo. Despite a higher male-biased operational sex ratio (OSR) in toads, the body lengths of the paired males and females were significantly correlated only in frogs. Increasing male-male competition, assessed via the OSR, resulted in a stronger correlation also in frogs only. Thus, great variability in the presence and intensity of SAM has been observed within both studied species.

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