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1.
Behavioral experiments have shown that male copepods of the species Tigriopus japonicus (Nori) can distinguish species, sex, and developmental stage of potential mates using contact chemoreception. Lectin-binding
patterns on the body surface of females have indicated that surface-bound glycoproteins may be important signals in mate choice.
In the present study, the proteolytic enzyme trypsin was used to cleave surface proteins from females, reducing their attractiveness
to males. The protein fragments released were used to make monoclonal antibodies. Three levels of screening were used to identify
monoclonal antibodies that recognized proteins involved in mate recognition. One monoclonal antibody bound to the terminal
urosome and lateral prosome of CV females, and its binding significantly decreased female attractiveness to males. Western
blotting showed that this antibody bound the trypsin-cleaved fragment and proteins of homogenized CV females and virgin adult
females, but did not bind proteins of homogenized males, CIII females, or females of T. californicus or T. fulvus. This antibody recognized proteins on the surface of females that may enable males to discriminate conspecifics, sex, and
age. It is likely that this molecule has a central role in the evolution of reproductive isolation in this group.
Received: 22 July 1999 / Accepted: 21 March 2000 相似文献
2.
Bi-directional sex change in a coral-dwelling goby 总被引:1,自引:0,他引:1
Philip L. Munday M. Julian Caley Geoffrey P. Jones 《Behavioral ecology and sociobiology》1998,43(6):371-377
Bi-directional sex change has recently been reported among obligate coral-dwelling gobies of the genus Gobiodon. However, neither the functional role of this pattern of sex change nor the frequency of sex change in either direction in
natural populations is known. We investigated the social structure and pattern of sex change of Gobiodon histrio at Lizard Island on the Great Barrier Reef. The social structure of G. histrio within coral colonies usually consisted of a single juvenile or a heterosexual adult pair. The size of adult social groups
was not constrained by coral colony size. In contrast to expectations for pair-forming species, G.␣histrio was primarily a protogynous hermaphrodite. All immature G. histrio were females and sex change from female to male occurred readily when two mature females were placed in a coral colony. In
addition, male G. histrio were able to change back to females when two mature males were placed in a coral. Sex change from female to male, however,
occurred with over twice the frequency of sex change from male to female. Where two males were placed in a coral colony, heterosexual
pairs were most frequently re-established by immigration of females from outside the treatment population. This pattern might
be predicted if sex change from male to female is more expensive than sex change from female to male for G. histrio. Where sex change is expensive, movement may be favoured over sex change, particularly where coral densities are high and
movement among corals incurs little mortality risk.
Received: 10 November 1997 / Accepted after revision: 16 May 1998 相似文献
3.
Several aspects of the biology of Bathypolypus sponsalis were studied from 297 individuals (115 males, 180 females and 2 indeterminates) caught in a depth range of 200–800 m depth
in the western Mediterranean Sea. The paper presents data on sizes (length-weight relationships, size-frequency distributions)
and reproduction (sex ratio, maturation, condition), and also analyses of the diet of B. sponsalis from samples taken throughout the year. Length-weight relationships showed that females are heavier than males at the same
mantle length. Although mature individuals were found all year round, the maximum number occurred in spring and summer. Sexual
maturation data revealed that males mature at smaller sizes than females. The gonadosomatic index increased with maturity
in both sexes; the increase was gradual in males, but abrupt in females. The digestive gland index was used as a condition
index and showed a differential behaviour with maturity; it increased gradually in females, but decreased in males. Like other
octopus species, B. sponsalis appears to be an opportunistic predator, feeding on a great variety of preys. Stomach content analysis yielded a total of
19 different prey items belonging to four major groups (Crustacea, Mollusca, Ophiuroidea and Osteichthya). The first three
groups were the more frequent preys, since crustaceans, molluscs and ophiuroids appeared in 76%, 49% and 30% of the stomachs,
respectively. Decapoda Reptantia (among crustaceans) and cephalopods and bivalves (among molluscs) constituted the more abundant
prey items. While the Decapoda Reptantia group was significantly more abundant in stomach contents of females, gastropods
were taken more frequently by males. These differences in diet could reveal females as a more active predators than males.
Received: 5 March 2000 / Accepted: 7 November 2000 相似文献
4.
Frequency and timing of extrapair fertilisation in the polyandrous red phalarope (Phalaropus fulicarius) 总被引:1,自引:0,他引:1
James Dale Robert Montgomerie Denise Michaud Peter Boag 《Behavioral ecology and sociobiology》1999,46(1):50-56
In sequentially polyandrous bird species, where females mate with different males in succession during a single breeding
season, sperm stored by females can occasionally lead to extrapair fertilisations (EPFs) in clutches cared for by the second
and subsequent males. Thus, we predicted that in red phalaropes (Phalaropus fulicarius) – a sex-role-reversed, sequentially polyandrous, arctic breeding shorebird – EPFs would occur more frequently in clutches
laid later in the breeding season. We used multilocus DNA profiling to examine the frequency and timing of EPFs in a population
of red phalaropes breeding in the Canadian high arctic. Using a technique to determine parentage without maternal DNA, we
inferred that 6 of 70 chicks in 18 broods resulted from EPFs – one extrapair chick in each of 6 broods. These results were
supported by a further analysis using microsatellite DNA. As predicted, broods containing EPFs hatched from clutches laid
significantly later in the season than did broods containing no EPFs. The difference in median hatch dates between broods
with and without EPFs was 9.0 days, or 38% of the entire egg-laying period in that season. For the whole breeding season,
we estimated that 6.5% of chicks were sired by extrapair males, which is similar to extrapair paternity estimates for other
sex-role-reversed birds, but relatively low compared to the majority of socially monogamous species studied so far.
Received: 24 August 1998 / Received in revised form: 18 January 1999 / Accepted: 24 January 1999 相似文献
5.
K. Reinhold 《Behavioral ecology and sociobiology》1996,39(3):189-194
Offspring sex ratio at hatching was examined in the bushcricket Poecilimon veluchianus. Offspring sex ratios varied significantly between females (Fig. 1). Low mortality prior to sex determination established
that this heterogeneity was already present in the primary offspring sex ratio. Sperm age and female age had no influence
on offspring sex ratio (Fig. 2). Male age at copulation, however, correlated significantly with offspring sex ratio (Fig. 3).
There were two types of males: one type produced predominantly daughters when young and an increasing proportion of sons with
age. The other type produced, independent of age, 1:1 offspring sex ratios (Fig. 4). The two types of males seem to occur
in approximately equal numbers. Sex ratio variation (1) may adaptively compensate for local sex ratio biases caused by sex-specific
motility, or (2) it may be adaptive if there is a sex-differential effect of laying date on offspring fitness.
Received: 14 March 1996/Accepted after revision: 24 June 1996 相似文献
6.
M. S. Mooring A. A. McKenzie Benjamin L. Hart 《Behavioral ecology and sociobiology》1996,38(4):259-266
The lesser mouse lemur (Microcebus murinus) is a prosimian primate which presents evidence of sex ratio bias of offspring that agrees with the direction of bias predicted
by the local resource competition model for facultative sex ratio adjustment. That is, females overproduced sons when grouped
prior to mating, whereas isolated females exhibited the opposite tendency. In this solitary species, social communication
relies heavily on urinary chemical signals. To test the hypothesis that sex biases induced by social factors may be linked
to urinary cues, isolated females were exposed (n = 76) or not (control group, n = 16) to urinary cues from other reproductively active females from the beginning of the breeding season (induced by long
photoperiod) until oestrus. During that period, females were either continuously (n = 17) or partially (n = 59) exposed to chemosignal stimulation. Females in oestrus were placed in contact with a breeding male and subsequently
isolated until they gave birth. All females entered oestrus but the timing of oestrus was significantly delayed by 1 week
in urine-exposed females. A general depressive effect of long-term urine exposure on fecundity was demonstrated, involving
fewer impregnations, higher abortion frequency and smaller litter sizes. Among females giving birth (n = 55) to a total of 129 young, a significant positive correlation was found between sex ratio bias towards males and the
duration of urine exposure. However, the shift in sex ratio at birth depended on the duration of urine stimulation during
a sensitive period extending from the beginning of the long photoperiod until the beginning of the follicular phase. In the
absence of urinary cues during the sensitive period, females significantly overproduced daughters (32% males of 53 newborn).
As urine exposure increased during the sensitive phase, the proportion of males in litters increased from 54% males (n = 50) in partially urine-exposed females to a significant bias towards males (69.2% of 26 newborn) in totally exposed females.
The biased sex ratio in response to chemical cues did not show consistent relationships with maternal body weight, parity
or litter size. Although the intrinsic mechanisms involved in sex-biased conceptions are not known, chemical cues could interact
with the photoperiodic control of gonadotropin secretions.
Received: 14 January 1995/Accepted after revision: 26 November 1995 相似文献
7.
The reproductive biology of spiny lobster, Panulirus penicillatus, was studied based on 2,068 lobsters, ranging from 34.28 to 131.60 mm carapace length (CL), sampled in Taitung coastal waters
from September 2003 to December 2004. The overall sex ratio approximated 1:1 (χ2 = 0.02, P > 0.05), but the monthly sex ratios in 2004 showed significant differences and males were predominant in sizes larger than
80 mm CL. Reproductive activity, assessed using histology, a gonadosomatic index and percentage of ovigerous females, indicated
that the mature females could be found in every month and that the major spawning occurred from May to September. The presence
of re-developing/re-ripe ovaries by month and size-specific spawning time suggest that larger mature females (>60 mm CL) spawn
at least three times a year while smaller new mature females spawn at least once a year. For females, the estimated sizes
at 50% physiological and functional maturity were (mean ± SE) 56.46 ± 0.56 mm CL and 66.63 ± 1.07 mm CL. The estimated sizes
at functional maturity were between 72 and 74 mm CL for males. The number of eggs per spawning event (brood size, BS) was
related to CL by the equation Y
BS = 2.4 × 10-3CL4.18 (r
2 = 0.902, n = 12). Female lobsters with CL ranging from 60 to 80 mm made the greatest contributions to egg production because of their
high brood size and active reproductive activity. A minimum legal size should be established for the fishery to protect egg
production potential of lobster population in the southeastern coastal waters off Taiwan. 相似文献
8.
Brood sex ratio is dependent on female mating status in polygynous great reed warblers 总被引:2,自引:0,他引:2
Isao Nishiumi 《Behavioral ecology and sociobiology》1998,44(1):9-14
Females capable of adjusting the sex ratio of their offspring should be more fit than females lacking such an ability. In
polygynous birds where breeding success in males is more strongly influenced by body size and/or attractiveness than in females,
females might produce more sons when predicting good conditions or when mating with attractive males. Polygynous great reed
warbler, Acrocephalusarundinaceus, males direct most of their feeding effort to the primary (first-hatching) nest and in these nests increase their feeding
effort in relation to the brood sex ratio (proportion of sons). Therefore, with the expectation of well-nourished sons, we
would predict that females which start breeding first within harems might produce more sons than those which start breeding
later, and in anticipation of sons with good genes, that females mated to polygynous males might produce more sons than females
mated to monogamous males. I took blood samples from hatchlings and determined the sex using DNA markers. The sex ratio of
primary (monogamous and polygynous primary) broods is more male-biased (mean 0.58 males, n = 50) than that of secondary (polygynous secondary and tertiary) broods (mean 0.46, n = 25). Moreover, in the secondary broods with the largest clutch (five eggs), in which offspring are most likely to suffer
food shortage, the sex ratio was distinctively female biased (mean 0.33, n = 10). In the primary broods, sex ratio was correlated to harem size. The results suggest that great reed warbler females
modify the brood sex ratio to produce both well-nourished sons and sons with good genes, but the former effect is probably
stronger than the latter factor.
Received: 11 March 1998 / Accepted after revision: 23 May 1998 相似文献
9.
The reproductive strategies of two gammaridean amphipod species, Gammarus wilkitzkii and Apherusa glacialis, that permanently inhabit the Arctic sea ice were investigated. G. wilkitzkii reaches sexual maturity at an age of 2 years and produces 128 ± 54 eggs fem.−1 yr−1. Mating takes place during fall and winter, and the development of the large eggs (0.60 to 0.80 mm diam.) lasts 6 to 7 months.
The sex ratio of G. wilkitzkii was dominated by males in a proportion of 1.5:1. In vivo studies showed that juveniles are released in batches from the brood
pouches of the females during April and May. A. glacialis reaches sexual maturity at the age of 1 year and produces 555 ± 151 eggs fem.−1 yr−1. The eggs are between 0.18 and 0.23 mm in diameter, and are the smallest known for gammaridean amphipods. Eggs are kept in
packages of two to eight in the brood pouches of females. The sex ratio of A. glacialis was dominated by females in a proportion of 3:1. The high fecundity of both amphipod species, the release of juveniles in
batches over a period of time, a high proportion of females (A. glacialis), and an elongated life-span with multiple spawnings (G. wilkitzkii) are discussed as possible adaptations to the specific and highly variable conditions under Arctic sea ice.
Received: 29 December 1999 / Accepted: 8 March 2000 相似文献
10.
A. D. Tucker H. I. McCallum C. J. Limpus K. R. McDonald 《Behavioral ecology and sociobiology》1998,44(2):85-90
We compared natal dispersals of freshwater crocodiles (Crocodylus johnstoni) against the prediction of male dispersal bias for a polygynous mating system. The crocodiles inhabited a linear series of
pools and we calculated the net distances from natal pools to recapture locations some 12–18 years later, at maturity. Philopatry
was assessed in terms of adult social distances. A female social distance was 0.46 pools and a male social distance was 1.0
pool. By these criteria, both sexes showed low levels of philopatry (7–12%). However, individuals of both sexes dispersed
from the natal site long before they were sexually mature. Divergence in dispersal patterns by sex occurred after the maturity
threshold, as males dispersed two to three times farther than females. Intrasexual competition by males is resolved by a size-based
hierarchy. The displacement of small males from local mating access is a probable cause of the longer dispersals undertaken
by males. Competition, rather than inbreeding avoidance, is driving dispersal in this population of freshwater crocodiles.
Received: 8 May 1998 / Accepted after revision: 26 June 1998 相似文献
11.
B. I. Bergström 《Marine Biology》1997,128(3):397-407
Based on demographic analysis of four different temporally enclosed demes of Pandalus borealis in Gullmarsfjorden on the Swedish west coast and published information, I discuss the notion of environmental sex determination
in protandric pandalid shrimps as suggested by sex allocation theory. Demographic results showed that age structure and mortality
rates varied substantially between four studied periods without noticeable effects on the age of sex change in the fjord populations.
The majority of shrimps changed sex at an approximate age of 3 years and became females at an age of 3 to 4 years, however,
low proportions (4 to 7%) of 2nd year females (transitional at ca. 1 year) and 3rd year females (5 to 12%) (transitional at
ca. 2 years) were present each year. Low proportions of primary females were also found in two of the temporally enclosed
demes, in 1985 (9%) and in 1987 (5%). These results do not indicate that yearly variations in age structure, mortality, or
frequency of older breeders in the breeding population affect the age of sex change in temporally enclosed fjord demes of
this protandric species. An alternative to assuming that the protandric mode of reproduction in pandalid shrimp is combined
with environmental sex determination is suggested.
Received: 24 September 1996 / Accepted: 6 November 1996 相似文献
12.
Condition-dependent control of paternity by female purple martins: implications for coloniality 总被引:9,自引:0,他引:9
Proposed causal links between extra-pair copulation (EPC) and colony formation in socially monogamous birds hinge on the
question of which sex controls fertilizations. We examined in colonial purple martins Progne subis (1) whether EPCs were forced or accepted by females, and (2) the degree to which apparently receptive females were able to
obtain EPCs against their mates’ paternity defenses. Paternity analyses of multilocus DNA fingerprinting confirmed previous
findings of a marked relationship between age class and extra-pair fertilizations (EPFs), with young males losing paternity
of 43% (n = 53) of their putative offspring compared to 4% (n = 85) by old males. All assignable extra-pair offspring were sired by old males, with one male obtaining most EPFs each year.
Contrary to the hypothesis that EPCs are forced, EPF frequency within age class did not increase with seasonal increases in
the number of males per fertile female. Whereas the male control hypothesis predicted that the male age class that mate-guarded
more would be cuckolded less, the reverse was true: young males guarded significantly more intensely. The male age class difference
in cuckoldry could not be explained by the possibility that young and inexperienced females (which are usually paired to young
males) were more vulnerable to forced copulation because EPFs were unrelated to female age. These findings suggest that females
(1) pair with old males and avoid EPCs, or (2) pursue a mixed mating strategy of pairing with young males and accepting EPCs
from old males. The receptivity to EPCs by females paired to young males put them in conflict with their mates. Two factors
determined the paternity achieved by young males: (1) the relative size of the male to the female, with young males achieving
much higher paternity when they were larger than their mates, and (2) the intensity of mate-guarding. Both variables together
explained 77% of the variance in paternity and are each aspects of male-female conflict. Given female receptivity to EPCs,
mate-guarding can be viewed as male interference with female mating strategies. We conclude that EPCs are rarely or never
forced, but the opportunity for females paired to young males to obtain EPCs is relative to the ability of their mates to
prevent them from encountering other males. Evidence of mixed mating strategies by females, combined with other features of
the martin mating system, is consistent with the female-driven “hidden lek hypothesis” of colony formation which predicts
that males are drawn to colonies when females seek extra-pair copulations.
Received: 23 March 1995/Accepted after revision: 14 January 1996 相似文献
13.
Association patterns of sailfin mollies (Poecilia latipinna): alternative hypotheses 总被引:3,自引:0,他引:3
Caitlin Gabor 《Behavioral ecology and sociobiology》1999,46(5):333-340
Individuals may associate with each other due to a variety of selective forces, such as intra- and intersexual selection,
and conspecific recognition. Previous studies have concluded that mate choice governs association behavior in polygynous species
of fish. I examined whether mate choice underlies the preference for larger individuals by examining preference for association
(time spent in proximity to a fish) not only between opposite-sex individuals but also between same-sex individuals of the
live-bearing sailfin molly (Poecilia latipinna). Males and females from three size classes were tested with a large and a small object fish of the same and opposite sex.
Females preferred to associate with larger over smaller males. Males also preferred to associate with larger over smaller
females, as expected. The same female and male test fish also preferred to associate with larger over smaller fish of the
same sex. Moreover, females demonstrated no significant difference in their strength of preference (large–small) when offered
males or females. The same held true for males. When males and females were subsequently tested with one large male and one
large female, females tended to prefer large males while males showed no significant preference for association based on sex.
In another experiment, females were tested with a large female and a small male, and significantly preferred the former. These
findings suggest that association patterns may have arisen under a variety of conditions, such as predation pressures, shoaling
behavior, and associative preference behavior. The assumption that association behavior is a uniformly sufficient predictor
of mate choice in fish needs to be re-examined for P. latipinna and other species.
Received: 6 November 1998 / Received in revised form: 12 May 1999 / Accepted: 12 May 1999 相似文献
14.
Norman Owen-Smith 《Behavioral ecology and sociobiology》1993,32(3):177-184
Summary Size dimorphism with males larger than females has been related to the benefits for males of enhanced dominance and hence reproductive success. However, mating gains must outweigh the fitness costs of deferred reproduction and the mortality associated with further growth. The relationships between male age, size and reproduction were assessed for greater kudus (Tragelaphus strepsiceros) in the Kruger National Park in South Africa. Individually identifiable animals were monitored over 10 years, with detailed observations made during six breeding seasons. In the non-breeding season males formed loose all-male groups. Horn grappling and low intensity agonistic interactions fostered dominance rankings. Dominance was age-graded, until males reached full weight at 6 years of age. Males aged 6 and 7 years monopolized courtship and mating, but 5-year-old males secured about 10% of mating opportunities. Few males survived beyond 7 years. Male mortality rate rose steeply with age, so that the functional sex ratio of fertile females per mature male was about 14:1. During the breeding season many female groups remained unattended by a mature male. Reproductive sorting among males occurred largely through variation in survival to full size and maturity. Increased size enhances fighting success and hence dominance. Further growth ceases when the functional sex ratio exceeds the number of mating opportunities that males can effectively achieve during a breeding season. Predation amplifies the mortality cost of continued growth. In the absence of large predators, male-male interactions may be atypically exaggerated. 相似文献
15.
Cecily M. Costello Scott R. Creel Steven T. Kalinowski Ninh V. Vu Howard B. Quigley 《Behavioral ecology and sociobiology》2009,64(1):125-134
We determined annual male reproductive success in black bears (Ursus americanus) using DNA and field data from two populations in New Mexico. We identified the likely father for 78 of 120 genotyped cubs
born during 1994–2000 and calculated reproductive success for 102 males known or presumed present within designated mating
regions. Age was a strong determinant of reproductive success. The observed peak in reproductive success occurred at roughly
the same intermediate age (10 years) as milder peaks in body size characteristics (11–12 years) and frequency of bear-inflicted
wounds (13 years), suggesting body size and fighting might be important for mating. Success was negatively associated with
the distance between home range centers of males and mothers. Success of young males (<7 years old) was also negatively associated
with mature male (≥7 years old) density, and increasing density shifted the peak age of reproduction higher. The dispersed
distribution of females likely limited the capacity of large mature males to dominate reproduction; therefore, success was
determined by a complex set of variables. 相似文献
16.
Catch and acoustic telemetry data were used to test three predictions of lekking behaviour in Atlantic cod (Gadus morhua L.) at a small-scale spawning ground (∼25 km2) in Placentia Bay, Newfoundland: (1) that cod form male-skewed aggregations during spawning; (2) spawning arenas occur at consistent sites; and (3) on the arenas, there will be higher proportions of spawning fish. Forty-two fishing sets from 1998 to 2003 indicated male-skewed sets early in the spawning season (April) in 5 of 6 survey years. Male-skewed sets were consistently distributed at depths < 50 m and mostly in one part of the ground. The proportions of spawning females and spent males were significantly higher in male-skewed sets, whereas sets with equal sex ratios had significantly higher proportions of immature males and spent females. In addition, cod of both sexes were significantly larger in male-skewed sets. Telemetric tracking of 25 cod in 2002 and 2003 (12 males, 13 females) indicated that both males and females were highly mobile while present on the spawning ground. Overall, our results add support to the hypothesis that cod employ a lekking mating system. 相似文献
17.
Christen E. Merte Thomas E. Goodwin Bruce A. Schulte 《Behavioral ecology and sociobiology》2010,64(3):401-408
Although communication is vital for members of a social species, the sexes may differ in the type and degree of information
sought. In many polygynous societies, males search for reproductively active females and compete intrasexually for access
to females with older males often being most successful. In social mammals, females may mature sooner than males and thus
at an earlier age behave more like adults. This maturation may include the assessment of potential mates directly or via indicative
signals. In this study, we observed the behavior of African elephants (Loxodonta africana) during their approach to waterholes. Waterholes provide an opportunity for elephants to investigate conspecific chemical
signals from feces and urine, and each other. We examined the presence of sexual dimorphism in behaviors of the trunk that
are indicative of olfactory investigation. We predicted that upon approach to a waterhole, adult males would show greater
interest than females in conspecific chemical signals. Females were predicted and observed to exhibit adult-like rates of
investigatory behavior at a younger age than males because females mature sooner. Adult males took the longest to reach the
waterhole in the last 100 m of approach; they also demonstrated greater investigatory rates to conspecific feces. Each sex
showed adult-type investigative behaviors with the trunk before the age of reproduction. Rather than showing a common chronological
developmental pattern across sex, the exhibition of investigatory, chemosensory behaviors reflected sex-specific changes in
reproductive development, perhaps reflective of the relative strength of intra- and intersexual selection on communication
patterns. 相似文献
18.
J. Fernando Márquez-Farías 《Marine Biology》2007,151(4):1445-1454
Guitarfishes are a primary component of artisanal elasmobranch fisheries and are commonly taken as trawl fishery bycatch throughout
the Gulf of California. However, little is known of the life history of this species. To address this lack of critical biological
information, the reproductive biology of Rhinobatos productus was investigated in the eastern Gulf of California. Development of claspers and testes indicated that males reach maturity
at 53 cm total length (TL). Measurements of oviducal gland, largest ovum diameter, and uterus width indicated that females
>57 cm TL are mature. This species possesses two functional ovaries: the ovarian cycle and gestation run concurrently. Histological
analysis of oviducal glands did not provide evidence of sperm storage, but females carrying uterine capsules were observed
over an extended period, suggesting the possibility of diapause in the early embryonic development. Following 4–5 months of
embryonic growth, pups were typically born from late June to October after a gestation period of approximately 11–12 months.
Width of yolk sac was inversely related to embryo length. The rate of reduction of yolk sac width suggests that embryos depend
on the sac until birth. Mean fecundity was estimated to be 5 (range 1–10, s.d. = 2.24) with a 1:1 sex ratio. Average size
at birth was 175 mm TL. Seasonally, gravid females enter shallow waters for parturition, becoming extremely vulnerable to
gill nets used in the artisanal ray fishery. 相似文献
19.
Female distribution affects mate searching and sexual selection in male northern water snakes (Nerodia sipedon) 总被引:2,自引:0,他引:2
Mating systems and sexual selection are assumed to be affected by the distribution of critical resources. We use observations
of 312 mating aggregations to compare mate-searching success of male northern water snakes (Nerodia sipedon) in two marshes in which differences in mating substrate availability resulted in more than fourfold differences in female
dispersion. Reproductive males had significantly larger home ranges where females were dispersed than where females were clumped.
The number of females encountered by males increased significantly with male home range size where females were dispersed,
and decreased significantly where females were clumped. Where females were clumped, males were more likely to encounter other
males when they located females. We found no evidence in either population that mate searching was energetically expensive
or that males with relatively more energy had larger home ranges. However, males with greater fat reserves at the start of
the season participated in more mating aggregations when females were dispersed, suggesting that fat reserves could affect
a male’s willingness to attempt mating or to persist in aggregations. When females were dispersed there was weak stabilizing
selection acting to maintain male body size (β=–0.14), but strong directional selection favoring larger (β=0.50) and fatter
(β=0.37) males. Over 7 years, the intensity of selection favoring larger males varied substantially (β=0.14–1.15), but that
variation was not related to variation in the operational sex ratio. We found no evidence of directional selection on either
body size (β=0.05) or fat reserves (β=0.10) of males when females were spatially clumped. Overall, the distribution of females
had a pronounced effect on male behavior, on the factors that affected male success in locating females, and probably on the
extent of sperm competition once females had been located.
Received: 23 November 1998 / Received in revised form: 9 August 1999 / Accepted: 18 August 1999 相似文献
20.
Repeated visual censuses of different categories (juveniles, females, territorial and group males) of the stoplight parrotfish
(Sparisoma viride, a protogynous hermaphrodite) over a 3-year period indicated a relatively stable size and structure of the adult population.
This allowed estimates of size-specific mortality, sex change, and territory acquisition probabilities from previously reported
growth rates. Comparison of the predicted number of survivors, sex changers, and territory take overs with field observations
indicates that our estimates are quite reliable. However, rather large differences in mortality are obtained for the largest
three size classes (>25 cm), which may be due to reduced accuracy of length estimates of large fish. A pooled mortality for
these classes is therefore suggested as a more realistic estimate. The life-history implications of our findings are investigated
by comparing the predicted survival and future reproductive success of fish that change sex at different sizes. Ten percent
of the adults reach an age of ca. 17 years, once a length of 20 cm is attained, as predicted from the pooled estimates. Calculations
based on these estimates indicate that the predicted reproductive output of a 15-year-old fish (2500 matings) is the same
for early (i.e. at 20 cm) and late (>30 cm) sex changers and for an average fish subject to the estimated daily sex change
and territory acquisition probabilities. These findings suggest that S. viride individuals are able to flexibly adjust the timing of sex change in an adaptive way to unpredictable local conditions. However,
independent mortality estimates are needed to corroborate our present findings.
Received: 2 January 1997 / Accepted: 27 January 1997 相似文献