Thermal biology of reproduction in viviparous skinks,Eulamprus tympanum: why do gravid females bask more?

Summary In some reptiles, gravid females bask more, and/or maintain higher body temperatures than do males or non-gravid females. This phenomenon is usually explained in terms of the female or her offspring benefitting from accelerated embryogenesis and early birth, but the effect of increased basking on gestation period has not been studied. In a laboratory experiment, gestation periods of gravid female skinks (Eulamprus tympanum) decreased with the duration of access to radiant heat. Embryonic development was more rapid in the laboratory than in the field, and there were no apparent adverse effects of this accelerated gestation on females or offspring. Number and mass of offspring, survival rates of embryos, relative clutch mass and female mass before and after parturition were not influenced by the decrease in gestation period caused by increased basking. Females selected similar temperatures in the laboratory and field (32° C), despite the availability of higher temperatures in the laboratory. Thus, gestation in the laboratory was accelerated by spending longer periods at usual basking temperatures, rather than by selecting higher temperatures. In the field, mean and modal body temperatures of active animals were similar in gravid females, males and non-gravid females, but gravid females appear to bask more of the time, even in cloudy weather when other members of the population do not bask. Hence, an apparent similarity in thermal regimes of gravid and non-gravid animals may mask significant underlying differences in thermoregulatory strategies.     

Reduction in locomotor ability as a cost of reproduction in gravid snakes

Summary Recent studies suggest that lower survival among gravid squamate reptiles may be partially the result of decreased locomotor ability during gestation. In this study, we compared the speed and endurance of female garter snakes (Thamnophis marcianus), before, during, and after pregnancy. Gravid snakes had significantly lower locomotor performance than did non-gravid females, and performance varied among stages of gestation, reaching a minimum 0–6 weeks prior to parturition. Both number of offspring and relative clutch mass were inversely correlated with locomotor performance; as females increased these traits, locomotor ability decreased. If reduced locomotor performance results in greater risk of predation and/or lowered foraging ability, then natural selection (operating via differential mortality or feeding rates of gravid females) may result in important constraints on both clutch size and relative clutch mass in squamates.     

Female affiliative preference depends on reproductive state in the African cichlid fish, Astatotilapia burtoni

Hormones play a pivotal role in reproductive behavior and havebeen implicated in mediating mate choice decisions. Here weasked whether the differences in female reproductive state dependenton changes in hormone levels correspond to changes in femaleaffiliation with males. In the African cichlid fish, Astatotilapiaburtoni, males shift between reproductive (territorial; T) andnon-reproductive (non-territorial; NT) states depending on socialcontext while females alternate between gravid (egg bearing;G) and non-gravid (NG) reproductive states independent of socialconditions. Moreover, the brain-pituitary-gonadal axis controllingreproduction and reproductive hormones is substantially remodeledin both males and females depending on reproductive state. Tomeasure affiliative preference, gravid and non-gravid femaleswere given the choice of associating with T or NT males. Gravidfemales preferentially associated with T males, whereas non-gravidfemales showed no preference. To discover whether gravid femalesuse male size independent of dominance status as a cue for theirchoice, gravid females were given a choice between territorialmales of different sizes. Gravid females preferred the smallerof two T males, but the smaller T males were significantly moreactive. Our results show that associative change could be animportant behavioral mediator between hormonal cues and reproductivesuccess, and that females use a hierarchy of cues in decision-making,preferring to affiliate with T over NT males and, among T males,preferring more active animals.     

Active foraging for toxic prey during gestation in a snake with maternal provisioning of sequestered chemical defences

Many animals sequester dietary defensive compounds and incorporate them into the offspring, which protects the young against predation. One possible but poorly investigated question is whether females of such species actively prey upon toxic diets. The snake Rhabdophis tigrinus sequesters defensive steroids from toads consumed as prey; it also feeds on other amphibians. Females produce chemically armed offspring in direct proportion to their own level of toad-derived toxins by provisioning the toxins to their eggs. Our field observations of movements and stomach contents of radio-tracked R. tigrinus showed that gravid snakes preyed upon toads by actively foraging in the habitat of toads, even though toads were a scarce resource and toad-searching may incur potential costs. Our Y-maze experiments demonstrated that gravid females were more likely to trail the chemical cues of toads than were males or non-gravid females. These results showed behavioural switching in females and active foraging for scarce, toxic prey during gestation. Because exploitation of toads by gravid females results in their offspring being more richly endowed with prey-derived toxins, active foraging for toxic prey is expected to be an adaptive antipredator trait, which may enhance chemical defence in offspring.     

Aspects of mating, reproduction, and co-occurrence in three freshwater calanoid copepods

SUMMARY. 1. We examined the seasonal distributions and mating behaviour of Epischura lacustris, Diaptomus minutus and Diaptomus oregonensis to evaluate several proposed mechanisms for reproductive isolation. There was no divergence in onset of maturity or timing of breeding periods between sympatric diaptomid populations; size displacement between co-occurring diaptomid species did not result in concomitant reduction in mating frequency between heterospecific pairs in the laboratory.
2. Divergence in mating behaviour was supported by observations that, in conspecific mating experiments, males of both diaptomid species discriminated between females bearing ripened ovaries (gravid) and those that did not (non-gravid), and that, in heterospecific trials, males either mated indiscriminantly with all females, or engaged in mating very infrequently.
3. In mating experiments with Epischura. males did not discriminate between gravid and non-gravid females, but mated exclusively with virgins of a specific relative size. Divergence in timing of breeding seasons between Epischura and the two diaptomid species suggests that even if mating between genera is possible, it does not occur often in nature.
4. We discuss the adaptive significance of different reproductive strategies of these three copepods and speculate on mechanisms that allow for coexistence of the closely related taxa in nature.     

Body temperature relationships in the lined snake,Tropidoclonion lineatum

• 1.1. Body temperatures of 69 adult lined snakes collected in the field were recorded along with associated air and substrate temperatures.
• 2.2. There was no difference between the mean body temperature of males and females or between gravid and non-gravid individuals.
• 3.3. Body temperatures differed significantly from either air or substrate temperatures.
• 4.4. Lined snakes appear to maintain an activity temperature range by use of selected microhabitats.

     

孕育对褶纹冠蚌滤食率的影响及鳃微结构变化

对比了褶纹冠蚌(Cristaria plicata)孕育蚌、未孕雌蚌和雄蚌的滤食率,并运用组织学、扫描电镜和透射电镜对实验蚌的鳃结构进行比较观察,以此探讨鳃结构变化对滤食功能的影响。滤食实验结果表明:孕育事件显著降低了雌蚌的滤食率,而未孕雌蚌与雄蚌的滤食率无显著差异。孕育雌蚌内外鳃均由两鳃小瓣愈合而成,每一鳃小瓣由成排的鳃丝组成,在中介区鳃丝之间通过丝间隔连接,在内部侧区则通过瓣间隔相连。雌蚌内鳃的鳃间隔为外鳃的2～3倍,而雄蚌的内外鳃无差异。孕育雌蚌外鳃在初级水管、瓣间隔等出现明显的变化,并出现了二级水管结构,而内鳃未发现显著变化。扫描电镜显示:在褶纹冠蚌鳃丝表面存在3种类型的纤毛(前纤毛、前侧纤毛和侧纤毛),其形态结构和分布各具特点,长径58～85μm椭圆形的鳃小孔成排相间分布于鳃丝之间,而3组实验蚌的内外鳃丝之间无明显差异。透射电镜观察发现:孕育雌蚌鳃丝表皮细胞表面形成突起,显著增加了表面微绒毛的数量,可能有利于雌蚌在孕育期间由于初级水管转化成育儿囊后对呼吸、滤食等功能的补偿,与其他蚌科物种报道类似。综合实验表明,孕育雌蚌外鳃结构的变化,尤其是初级水管的结构改变和二级水管、鳃丝表面褶皱的出现可能是影响孕育雌蚌滤食功能的主要原因。     

Mate location by diaptomid copepods

Female diaptamid copepods oscillate frequently between gravidand non-gravid conditions (about every 4 days at 18°C, inthose species tested). Since viable egg sacs have been producedonly by females mated during the gravid phase of this cycleand since remating is required for each clutch, experimentswere conducted to determine whether mate selection was relatedto the reproductive condition of females, thus maximizing reproductiveeffort. The results indicated that males pursue and attemptto mate with any congener approached caudally, apparently usinga hydrodynamic signal in the swimming wake as an initial cue,but they are most successful in catching gravid females. Theseresults suggest the existence of a discriminatory mechanismwhich is linked to the female's reproductive cycle. The purportedmechanism operates after a potential mate is initially perceived,and it may involve a modification of the female's escape behavioror the production of a pheromone. Further attempts to definethe mechanism should concentrate on differences between gravidand non-gravid females. ¹Present address: R.M. Parsons Laboratory, 48-429, MassachusettsInstitute of Technology, Cambridge, MA 02139, USA.     

Effects of incubation temperature on hatchling phenotypes in an oviparous lizard with prolonged egg retention: are the two main hypotheses on the evolution of viviparity compatible?

Females of several lizard species modify their body temperature during pregnancy, probably in connection with the optimisation of hatchling phenotypes. We studied variations in the temperature selected by gravid females compared with those selected by males and non-gravid females in an oviparous population of Zootoca vivipara (Jacquin, 1797) (Squamata: Lacertidae) of Northern Spain and examined the effects of incubation temperature on the phenotypic variation of hatchlings. Cloacal temperatures of gravid females active in the field were lower than those of males and non-gravid females, as well as the temperatures selected in a thermal gradient created in the laboratory (mean±s.d.: 32.33±1.27 °C for gravid females; 34.05±1.07 °C for males and non-gravid females). Effects of temperature were assessed by incubating eggs at five constant temperatures (21, 25, 29, 32 and 34 °C). Incubation time decreased as temperature increased, following a negative exponential function. Incubation temperatures also affected the hatchlings’ morphology: hatchlings incubated at 34 °C had shorter heads than those from other temperatures. Survival at 34 °C (58%) was significantly lower than at the other temperatures (mean 93%). Pregnant females select lower body temperature, approaching the temperatures that optimise hatchling phenotypes, according to predictions of the maternal manipulation hypothesis on the evolution of viviparity. The shift in preferred temperature by pregnant females would result in only a very short delay, if any, of hatching time and, because the temperature selected by pregnant females is much higher than average temperatures recorded in natural nests of Z. vivipara, egg retention considerably shortens incubation time, according to predictions of the cold-climate hypothesis. Our experimental results indicate that the two main hypotheses on the evolution of viviparity are compatible in our study model.     

Shift in Thermal Preferences of Female Oviparous Common Lizards During Egg Retention: Insights into the Evolution of Reptilian Viviparity

Pregnant female Zootoca vivipara select lower body temperatures than males or nonpregnant females, and this shift in the thermal preferendum is believed to be related to optimising the conditions for embryogenesis. Thus, subjecting embryos to the higher temperature selected by males and non-gravid females might have detrimental effects on embryonic development and on hatchling fitness, according to predictions of the “maternal manipulation” hypothesis on the evolution of viviparity. To test the role of gestation environment on embryonic development in oviparous Z. vivipara, we kept a number of gravid females at the temperature selected by non-gravid females in a laboratory thermal gradient, whereas control females were allowed to regulate their body temperature without restrictions. Developmental stage at oviposition was more advanced for embryos of the experimental clutches, which were heavier than those of the control group. Forced gestation temperature also affected hatching success (58.62% in the experimental treatment vs. 97.37% in the control group). In addition, hatchlings from females subjected to high temperatures during pregnancy were smaller, had shorter head length and performed worse in running trials. Our results fulfil the prediction of the “maternal manipulation” hypothesis, and suggest that the shift in female body temperature during pregnancy optimizes embryogenesis and hatchling phenotype by avoiding the negative effects of the high incubation temperatures preferred by non-gravid females.     

Relationships between sexual dimorphism and niche partitioning within a clade of sea-snakes (Laticaudinae)

Previous studies in Fiji have shown that females of the amphibious sea-krait Laticauda colubrina are much larger than males, and have larger heads relative to body size. The dimorphism has been interpreted in terms of adaptation to a sex divergence in prey-size: females primarily eat large (conger) eels rather than smaller (moray) eels. The hypothesis that dimorphism is affected by niche divergence predicts that the degree of sex dimorphism will shift when such a species invades a habitat with a different range of potential prey sizes. On the island of Efate in Vanuatu, L. colubrina and a regionally endemic sibling species (L. frontalis) both consume smaller eels (in absolute terms, and relative to the snake's body size) than do the previously-studied Fijian snakes. Patterns of morphology and sexual dimorphism have shifted also. Both Vanuatu taxa are slender-bodied, and frontalis is smaller and less dimorphic than L. colubrina. Females grow larger than males in all taxa, and have larger heads (relative to body length), but the degree of sexual divergence is lower in Vanuatu (especially in frontalis). Dietary overlap (in prey species as well as size) is high between adult frontalis and juvenile colubrina, but the two taxa differ in prey size/predator size relationships. In particular, male frontalis eat very small prey and have very short heads. Our results are consistent with the hypothesis that sex differences in the mean adult body sizes and relative head sizes of laticaudine snakes are linked to sex differences in feeding biology.     

Effects of gravidity on habitat use and antipredator behaviour in three-spined sticklebacks

Habitat use was examined in six Alaskan populations of three-spined sticklebacks Gasterosteus aculeatus . In three lakes with predatory fishes, gravid female sticklebacks remained closer to refuge than did non-gravid females, while those in lakes devoid of piscivores did not display this shift in behaviour. Gravid females in a lake with predatory rainbow trout Oncorhynchus mykiss used different evasive manoeuvres than did non-gravid females during in situ encounters with a model rainbow trout. Gravid females were more likely to incorporate a protean element in their flight moffements than were non-gravid females. Offerall, these data suggest that gravid female three-spined sticklebacks modify habitat use and escape behaviour to reduce vulnerability to predators.     

Mate Choice by Chemical Cues in Western Redback (Plethodon vehiculum) and Dunn's (P. dunni) Salamanders

Western redback and Dunn's salamanders (Plethodon vehiculum and Plethodon dunni, respectively) can distinguish between potential mates by using chemical cues. In laboratory choice tests, adult males of both species showed significant discrimination between chemical cues of gravid females over non-gravid females of equal body size. Furthermore, males of both species differentiated the odour of paired gravid females that differed by ? 5 mm snout-vent length (SVL). Given that clutch size is related to female body size in these species, adult males may be able to distinguish between females via cues that signal potentially high female reproductive success. In choice tests, P. vehiculum females did not discriminate between two relatively large males that differed by ? 5 mm SVL. However, females of P. vehiculum did discriminate between two relatively small males that differed by the same amount. Apparently, P. vehiculum females ranked males by both absolute and relative body size using chemical cues. This pattern could reflect a female preference for large males or that females avoid mating with the smallest males.     

Alternative mating tactics in the yellow dung fly: resolving mechanisms of small-male advantage off pasture

Recent work suggests that the yellow dung fly mating system may include alternative patroller–competitor mating tactics in which large males compete for gravid females on dung, whereas small, non-competitive males search for females at foraging sites. Small males obtain most matings off pasture, yet the behavioural mechanism(s) giving rise to this pattern are unknown. We investigated the male and female behaviours that determine mating success in this environment by conducting field mating experiments and found small males to benefit from several attributes specific to the off-pasture mating environment. First, small males from foraging sites exhibited higher mating propensity, indicating that large males away from dung may be depleted of energy and/or sperm. Second, small males were more discriminating, being significantly less likely to attempt with non-gravid females, which are absent on dung but common off pasture. Third, non-gravid females were generally more likely to actively struggle and reject mating attempts; however, such behaviours occurred disproportionately more often with large males. Female Scathophaga stercoraria thus appear to preferentially mate with small males when off pasture. These findings challenge assumptions about male–female interactions in systems with alternative mating tactics and reveal hidden processes that may influence selection patterns in the field.     

Rattling Behavior of Prairie Rattlesnakes (Crotalus viridis viridis,Viperidae) in Relation to Sex,Reproductive Status,Body Size,and Body Temperature

We examined whether sex, reproductive status, body size, or body temperature of prairie rattlesnakes (Crotalus viridis viridis) was related to when snakes rattled in response to an approaching observer. We found that gravid females allowed significantly closer approaches than males, suggesting that females relied on crypsis to avoid predation, possibly because pregnancy constrained their locomotive ability. Smaller snakes allowed significantly closer approaches than did larger snakes. Smaller snakes may be more cryptic or slower, which may influence their waiting to rattle until the observer was close. Overall, we found no consistent relationship between the distance from the observer that a snake rattled and its body temperature. However, cooler gravid females allowed closer approaches by the observer than did warmer gravid females. In summary, reproductive status, body size, and body temperature appear to influence the costs and benefits of crypsis vs. active defense of rattlesnakes.     

Intra-population variability in energy parameters of the salamander Plethodon Cinereus

Summary Mean values of energetic parameters are used in ecosystem studies because only crude estimates are possible when dealing with a large scope. However, when the focus is at the population level, finer resolution is possible and thus potential ontogenetic differences should be examined. Analysis of energetic parameters of a population of terrestrial salamander, Plethodon cinereus, was undertaken in order to determine ontogenetic differences.Digestive efficiency does not differ significantly between age classes, nor is it correlated with energy intake. Adult males and non-gravid females have virtually identical mean efficiencies. Thus it is probably meaningful to calculate energy flow through the population using a mean digestive efficiency value. Percent water content decreases significantly with increasing age whereas percent ash content increases significantly. Thus when estimating energy tied up in standing crop, correction must be applied for ontogenetic differences in water and ash content. Once these corrections have been made, the AFDW-specific energy content is not significantly different between age groups (with the exception of gravid females which is higher). Salamanders accumulate energy in their tissues with increasing age, although immatures are not significantly different from non-gravid adults. Since gravid females have significantly more joules/mg wet weight than other groups, separate energy density values must be calculated for these individuals if a meaningful standing crop energy estimate is to be obtained from wet weight biomass.     

Male mate choice in the Andrew’s toad <Emphasis Type="Italic">Bufo andrewsi</Emphasis>: a preference for larger females

In amphibians, theory predicts that male mate choice with respect to female body size can be expected to occur when female fecundity is related to body size and when the time and energy invested into one mating are relatively large. Based on experimental observations, we tested whether male mate choice occurs in a population of the Andrew’s toad (Bufo andrewsi), a species in which both assumptions are likely to be met. When a male B. andrewsi was placed with a gravid female and a non-gravid similar-sized female, the male did not discriminate between them. When two gravid females with distinct size differences were provided to a male, the male preferred the larger one. In an experiment in which two different-sized gravid females were put in two separate transparent cylinders to exclude potential chemical cues, males spent more time in proximity to the larger gravid females and jumped more frequently towards the larger gravid females than the smaller ones. These findings suggest that male B. andrewsi recognizes female body size, exhibits mate choice, and prefers to mate with larger females that provide greater reproductive potential.     

Body mass changes inTrimeresurus flavoviridis (Viperidae) on Okinawa Island,Japan

Body masses of wild-caught habu,Trimeresurus flavoviridis, were measured with known error range. Habu larger than mature female size had steeper slope in length-mass regression than smaller individuals. Females outweighed males in most snout-ventlength classes and in early summer. Gravid females outweighed non-gravid ones by about 20% on the average, but the body mass ranges of the two groups overlapped. Through the body mass change in mature females, the proportion of gravid females was estimated to be about 0.5.     

The effect of the acanthocephalan parasite Pomphorhynchus laevis on the lipid and glycogen content of its intermediate host Gammarus pulex

Besides conspicuous changes in behaviour, manipulative parasites may also induce subtle physiological effects in the host that may also be favourable to the parasite. In particular, parasites may be able to influence the re-allocation of resources in their own favour. We studied the association between the presence of the acanthocephalan parasite, Pomphorhynchus laevis, and inter-individual variation in the lipid and glycogen content of its crustacean host, Gammarus pulex (Amphipoda). Infected gravid females had significantly lower lipid contents than uninfected females, but there was no difference in the lipid contents of non-gravid females and males that were infected with P. laevis. In contrast, we found that all individuals that were parasitised by P. laevis had significantly increased glycogen contents, independent of their sex and reproductive status. We discuss our results in relation to sex-related reproductive strategies of hosts, and the influence they may have on the level of conflict over energy allocation between the host and the parasite.     

Territorial behavior of the plethodontid salamander Plethodon kentucki: influence of habitat structure and population density

To investigate the possible influence of variation in ecological and demographic factors on the spatial organization of the terrestrial plethodontid salamander Plethodon kentucki, I conducted a 3-year capture-recapture study and determined home-range characteristics and spatial relationships of individuals at two field sites that differed in predominant cover type and population density. Home ranges of adults were fixed and the home ranges of same-sex adult neighbors were mostly exclusive. The spatial arrangement of adult home ranges exhibited overall regularity or regularity within aggregations, whereas the distribution of juvenile home ranges was usually random. Analysis of nearest-neighbor sex indicated a positive intersexual association of adult home ranges. Removal studies provided evidence for defense of adult home ranges only at the high-density site. The distribution of home ranges was influenced by the presence of cover objects, but there was no significant relationship between adult body size and percent of home-range area with cover. Males overlapped the home ranges of gravid females significantly more often than those of non-gravid females, indicating that the distribution of gravid females had a strong influence on the distribution of male home ranges. In laboratory tests, increased male-male aggression during the breeding season suggests that males may compete for access to mates. At the high-density site, larger males may have benefited by having greater reproductive success than smaller males because they were more dominant and their home ranges overlapped a greater number of gravid-female home ranges. My results indicate that habitat structure and population density may influence the spatial organization and mating system of P. kentucki. Received: 26 May 1997 / Accepted: 9 October 1997