Genital morphology linked to social status in the bank vole (<Emphasis Type="Italic">Myodes glareolus</Emphasis>)

Since genital morphology can influence the outcome of post-copulatory sexual selection, differences in the genitalia of dominant and subordinate males could be a factor contributing to the fertilisation advantage of dominant males under sperm competition. Here we investigate for the first time if penile morphology differs according to male social status in a promiscuous mammal, the bank vole (Myodes glareolus). In this species, dominant males typically achieve higher reproductive success than subordinates in post-copulatory sexual selection, and male genital morphology is complex, including both a baculum (os penis) and penile spines. Our results show that despite no difference in body size associated with male social status, baculum width is significantly larger in dominant male bank voles than in subordinates. We also found evidence of positive allometry and a relatively high coefficient of phenotypic variation in the baculum width of male bank voles, consistent with an influence of sexual selection. By contrast, baculum length and three measures of penile spinosity did not differ according to male social status or show evidence of positive allometry. We conclude that dominant male bank voles may benefit from an enlarged baculum under sperm competition and/or cryptic female choice and that differences in penile morphology according to male social status might be important but as yet largely unexplored source of variation in male reproductive success.     

Regional differences in behaviour in bank voles (Clethrionomys glareolus): dyadic encounters

North Scandinavian bank voles (Clethrionomys glareolus) differ from south Scandinavian conspecifics both in population dynamics and in activity, social behaviour, density-related sensitivity in sexual maturation and in reproduction. Some ecologists think that cyclically fluctuating rodents are particularly aggressive, at least in certain cycle phases. This hypothesis was tested in dyadic encounters between animals from southern and northern Sweden, respectively. Univariate analyses showed significant differences between regions in four separate behavioural traits, but not in behaviour related to aggression. Laboratory breeding for several generations did not affect the level of aggressivity. Multivariate analyses revealed two main components of activity and sociability, both with regional variation. Activity components (also including “freezing” behaviour) were chiefly related to age while sociability showed mainly regional variation. Differences observed may be due to the geographic location or earlier cyclicity, as the cyclic pattern was weak at the time when the test animals were sampled. An adaptation to high-density situations appears likely as the sympatric field vole (Microtus agrestis) shows similar regional differences although it lives in a different habitat. Cyclic animals appear to disperse at increasing densities while non-cyclic animals show clumped distributions. Received: 19 February 1996/Accepted after revision: 17 August 1996     

Infanticide in seasonally breeding multimale groups of Hanuman langurs (Presbytis entellus) in Ramnagar (South Nepal)

In the seasonally breeding langur (Presbytis entellus) population of Ramnagar, South Nepal, where multimale groups prevail, 25 attacks on 11 infants (including one actual killing) by seven adult males were witnessed in five groups by six observers between 1990 and 1996. Circumstantial evidence also indicates three additional attempts at infanticide and in seven additional cases infanticide was presumed or likely. Infanticide presumably accounted for 30.8–62.5% of infant mortality in the first 2 years of life. Most attackers (91.4%) were residents of the infants' group and had immigrated after the infants had been born (75.0%) or conceived (25.0%). Thus, they were not related to the victims. The interbirth interval was shortened if an infant died either prior to September of its 1st year of life (mean = 1.2 years), or its 2nd year (mean = 2.0) and even its 3rd year (mean = 2.4). All attackers remained in the group at least until the next mating season; high-ranking males maintained their dominance rank and lower-ranking males rose in rank. Since rank and mating success were correlated and rank and reproductive success might be correlated, all attackers had a good chance of siring the next infant of the victims' mothers and could thus have benefited by their action. Infanticide seems to be a male reproductive strategy at Ramnagar. Infanticide has never before been reported among seasonally breeding langurs living at such low densities. This is also the first detailed report of infanticide as a male reproductive strategy in a seasonally breeding primate population. Received: 19 December 1996 / Accepted after revision: 7 June 1997     

Do female bank voles (Clethrionomys glareolus) mate multiply to improve on previous mates?

Contrary to classical sexual selection theories, females of many taxa mate with multiple males during one reproductive cycle. In this study, we conducted an experiment on the “trade-up hypothesis”, which proposes that females remate if a subsequently encountered male is potentially superior to previous mates to maximize the genetic quality of their offspring. We presented bank vole females (Clethrionomys glareolus) sequentially with two males of known dominance rank in different orders, i.e., either first subordinate and second dominant, first dominant and second subordinate, or two males that were equal in dominance (high ranking) and observed their mating behavior. We found that 92% of the females mated multiply and did not base their remating decision on male social status. Therefore, polyandry cannot be explained by the “trade-up hypothesis” based on dominance rank in this species. However, we found that dominant males sired significantly more offspring than subordinate males. This varied according to mating order: dominant males sired more offspring when they were second than when they were first. Moreover, litter sizes were significantly smaller when the dominant male was first (smallest relative success of dominant males) compared to litter sizes when mating order was reversed or both males equal in status. Our results suggest that even though multimale mating includes males that are of poorer quality and thus potentially decreases the fitness of offspring, most of a female’s offspring are sired by dominant males. Whether this is due to cryptic female choice, sperm competition, or a combination of both, remains to be tested.     

Condition dependence of sexual attractiveness in the bank vole

The capture of genetic variation by sexual traits due to their condition dependence is hypothesized to underlie the genetic benefits of mate choice. Here, we investigate condition dependence of sexual attractiveness of bank vole Myodes glareolus males by manipulating their diet during the period of maturation. We find that reducing diet quality negatively affected both male mating success and development of preputial glands used in sexual signaling. Preputial glands showed stronger condition dependence than other organs measured (testes, heart, intestines). In contrast to mating success, male dominance was not significantly affected by diet manipulation and was not correlated with male mating success. Thus, our results support condition dependence of sexual attractiveness but not of intrasexual competitiveness.     

Female bank voles (Clethrionomys glareolus) prefer dominant males; but what if there is no choice?

Both intra-sexual competition between males and female mate choice have been found to affect mating behaviour in rodents. We studied female choice in the bank vole (Clethrionomys glareolus) under circumstances where male-male competition was excluded and the female could interact and mate freely with the males. Mating behaviour was observed in two situations: (1) the female encountered two males with a clear dominance relationship; and (2) the two males were equal in their social status. In all tests where a female in postpartum oestrus had a choice between males of different social rank she mated with the dominant one. When choosing between an even pair of males there was no difference in the frequency of lordotic responses, mounts or intromissions the female exhibited with either male before mating with one of them. The mean ejaculation latency was significantly longer in the tests with an even pair of males than in the tests where male hierarchy was clear. These results show that bank vole females are able to discriminate males according to their social status and strongly prefer dominant males as mating partners. However, when the females were presented with two equal males, they seemed to be unable to make a choice. The ability to choose the mating partner when the males are clearly different may be an important direct benefit for the female in terms of time saved during mating and thus decreased risk of predation and infanticide. Received: 16 March 1995/Accepted after revision: 11 February 1996     

Diving behavior of immature hawksbills (Eretmochelys imbricata) in a Caribbean cliff-wall habitat

Time-depth recorders were attached to immature hawksbills (Eretmochelys imbricata Linnaeus, 1766) residing at the northwestern cliffs of Mona Island, Puerto Rico. Data on diving profiles obtained from four turtles of 32.0 to 53.4 cm straight carapace length revealed strong similarities in behavioral patterns. During daylight hours, turtles were active an average 8.4 h per day, surfacing 3.6% of the time. Length of foraging dives correlated with turtle size, with mean durations ranging from 8.6 to 14.0 min. Foraging dives, with a mean depth of 4.7 m, were associated with feeding on encrusting sponges. At night, turtles were mostly inactive, surfacing 1.8% of the time and with individual mean submergence intervals of between 30.4 and 37.1 min. From the surfacing behavior of turtles making deep and long dives, it is inferred that dives were aerobic, with the turtles making use of oxygen stores in addition to that of the lung.     

Thermal effects on swimming activity and habitat choice in juvenile Pacific cod (Gadus macrocephalus)

The behavioral responses of fishes to temperature variation have received less attention than physiological responses, despite their direct implications for predator–prey dynamics in aquatic ecosystems. In this paper, we describe the temperature dependence of swimming performance and behavioral characteristics of juvenile Pacific cod (Gadus macrocephalus; 75–125 mm total length). Maximum swimming speeds increased with temperature and body size. Routine swimming speeds of Pacific cod in small groups of similarly sized fish (N = 6) increased with body size and were 34 % faster at 9 °C than at 2 °C. The response to temperature was opposite that previously described for juvenile walleye pollock (Theragra chalcogramma), reflecting species-specific differences in behavioral responses. In a separate experiment, we demonstrated the effect of temperature on habitat selection of juvenile Pacific cod: Use of an artificial eelgrass patch in a 5-m-long laboratory tank was significantly greater at 9 °C than at 2 °C. These results illustrate that temperature affects a range of behavioral traits that play important roles in determining the frequency and outcomes of predator–prey interactions.     

Comparison of diving behavior and foraging habitat use between chinstrap and gentoo penguins breeding in the South Shetland Islands, Antarctica

Chinstrap, Pygoscelis antarctica, and gentoo, P. papua, penguins are sympatric species that inhabit the Antarctic Peninsula. To evaluate differences in the foraging habitat of these two species, we recorded their foraging locations and diving behavior using recently developed GPS-depth data loggers. The study was conducted on King George Island, Antarctica during the chick-guarding period of both species, from December 2006 to January 2007. The area used for foraging, estimated as the 95% kernel density of dive (>5 m) locations, overlapped partially between the two species (26.4 and 68.5% of the area overlapped for chinstrap and gentoo penguins, respectively). However, the core foraging area, estimated as the 50% kernel density, was mostly separate (12.8 and 25.0% of the area overlapped for chinstrap and gentoo penguins, respectively). Chinstrap penguins tended to use off-shelf (water depth > 200 m) regions (77% of the locations for dives >5 m), whereas gentoo penguins mainly used on-shelf (water depth < 200 m) areas (71% of dive locations). The data on foraging locations, diving behavior, and bathymetry indicated that gentoo penguins often performed benthic dives (28% of dives >5 m), whereas chinstrap penguins almost always used the epipelagic/mid-water layer (96% of dives >5 m). Diving parameters such as diving bottom duration or diving efficiency differed between the species, reflecting differences in the use of foraging habitat. The diving parameters also suggested that the on-shelf benthic layer was profitable foraging habitat for gentoo penguins. Conversely, the relationship between trip duration, date, and stomach content mass suggested that the chinstrap penguins went further from the colony to forage as the season progressed, possibly reflecting a reduction in prey availability near the colony. Our results suggest that chinstrap and gentoo penguins segregated their foraging habitat in the Antarctic coastal marine environment, possibly due to inter- and intra-specific competition for common prey resources.     

Dominions and site-fixed aggressive behavior in breeding male Leucorrhinia intacta (Odonata: Libellulidae)

Summary We report aggressive spacing behavior in male dragonflies, Leucorrhinia intacta, that is characterized by variations in the probability of chasing conspecific male intruders within a defined area around a male's perch. The chase probability depends on the total intruder pressure and the behavior and distance of the intruder from the perched male (Fig. 2). This nonexclusive, site-fixed area has been called a dominion.We also examined the distribution of intruders among the various behavior-distance categories. Chase rates (per 15 min) were correlated mostly with number of intruders that hovered (rather than flew) close to the territorial male. Finally, we examined the impact of the changing chase probabilities on the variation in aggressive interactions as a function of intruder pressure. We conclude that, to some extent, territorial males stabilized defense costs across a variety of intruder pressures by maintaining dominions.     

Using experimental reintroductions to resolve the roles of habitat quality and metapopulation dynamics on patch occupancy in fragmented landscapes

Declines of species in fragmented landscapes can potentially be reversed either by restoring connectivity or restoring local habitat quality. Models fitted to snapshot occupancy data can be used to predict the effectiveness of these actions. However, such inferences can be misleading if the reliability of the habitat and landscape metrics used is unknown. The only way to unambiguously resolve the roles of habitat quality and metapopulation dynamics is to conduct experimental reintroductions to unoccupied patches so that habitat quality can be measured directly from data on vital rates. We, therefore, conducted a 15-year study that involved reintroducing a threatened New Zealand bird to unoccupied forest fragments to obtain reliable data on their habitat quality and reassess initial inferences made by modeling occupancy against habitat and landscape metrics. Although reproductive rates were similar among fragments, subtle differences in adult survival rates resulted in λ (finite rate of increase) estimations of <0.9 for 9 of the 12 fragments that were previously unoccupied. This was the case for only 1 of 14 naturally occupied fragments. This variation in λ largely explained the original occupancy pattern, reversing our original conclusion from occupancy modeling that this occupancy pattern was isolation driven and suggesting that it would be detrimental to increase connectivity without improving local habitat quality. These results illustrate that inferences from snapshot occupancy should be treated with caution and subjected to testing through experimental reintroductions in selected model systems.     

Modeling the dynamic habitat and breeding population of Southwestern Willow Flycatcher

To aid in the management and conservation of Southwestern Willow Flycatcher (Empidonax traillii extimus, hereafter “Flycatcher”), we developed numerous models of flycatcher breeding habitat at Roosevelt Lake, AZ. For model development and testing, we compiled 10 years of flycatcher territory data that were obtained from intensive fieldwork between 1996 and 2005. We identified riparian vegetation annually in the project area from Landsat Thematic Mapper images, and extracted floodplain features from a digital elevation model. We created a novel class of temporal (i.e., multiyear) variables by characterizing the stability and variability in breeding habitat over a 6-year time interval. We used logistic regression to determine associations between environmental variables and flycatcher territory occurrence, and to test specific hypotheses. We mapped the probability of territory occurrence with a GIS and determined model accuracies with a classification table and a 10-year population database. Environmental features that were associated with breeding flycatchers included floodplain size, proximity to water, and the density, heterogeneity, age and stability of riparian vegetation. Our best model explained 79% of the variability in the flycatcher breeding population at Roosevelt Lake. The majority of predicted flycatcher habitat formed between 1996 and 2004 on an exposed lakebed ～3 years after water levels receded during a prolonged drought. A high correlation between annual reservoir levels and predicted breeding habitat (r = ?0.82) indicates that we can create and manage habitat for conservation purposes. Our predictive models quantify and assess the relative quality of flycatcher breeding habitat remotely, and can be used to evaluate the effectiveness of habitat restoration activities. Numerous techniques we developed can be used to characterize riparian vegetation and patch dynamics directly off of satellite imagery, thereby increasing its utility for conservation purposes.     

Age-specific social dominance affects habitat use by breeding American redstarts (Setophaga ruticilla): a removal experiment

Summary By removing older males from their breeding territories, we tested the hypothesis that age-related dominance behavior influenced the pattern of habitat selection by breeding American redstarts Setophaga ruticilla (Aves: Parulinae). Fifteen older male redstarts removed in five experimental replicates during three breeding seasons were replaced by ten yearling and five older males; no redstart males of either age colonized the control sites during the same time periods, although two yearlings disappeared. Significantly more yearling males (67%, n=9) colonized the vacated areas than were present in the redstart population at large (26.8%, n=209). We reject the alternative hypothesis that yearling male redstarts occupy different habitats from older males because of age-related (innate) habitat preferences. Redstarts that colonized the territories made vacant by our removals (i.e., floaters) were a behaviorally heterogeneous group of animals. The presence of both yearling and older male floaters indicates that suitable habitat is limiting for this species and that intraspecific competitive interactions are important in habitat distribution, and potentially in population regulation.     

Distribution,habitat preferences and breeding periods in the crustaceans Sesarma cinereum and S. reticulatum (Brachyura: Decapoda: Grapsidae)

The distribution and habitat preferences of Sesarma cinereum and S. reticulatum were studied in the region of Beaufort, North Carolina, USA. S. cinereum inhabits the supralittoral zones of marshes characterized by high salinities (mean=27.9%) and sandy substrates, while s. reticulatum were found to prefer eulittoral marshes with brackish salinities (mean=16.2%) and silty substrates. Major differences have also been found in the cycling of egg production between these two species. Populations of S. cinereum produce approximately 4 to 6 egg batches in close synchrony with the lunar phase, whereas populations of S. reticulatum produce only from 2 to 3 batches of young per breeding season. It appears that female S. cinereum invest less time in carrying their eggs (approximately 1 lunar month), while female S. reticulartum invest a greater amount of time (eggs carried for approximately 45 days). These and other specific differences in reproductive strategies suggest that populations of S. cinereum are responding to density-independent selective pressures, while populations of S. reticulatum exhibit characteristics of density-dependent selective effects.     

The anxious vole: the impact of group and gender on collective behavior under life-threat

Social animals behave collectively in order to maintain a cohesive group. This collective behavior is often led by a few individuals of specific gender, social rank, or spatial physical location in the group (i.e., perimeter or front). We examined how individual social voles (Microtus socialis) in same-gender compared with mixed-gender groups respond to an owl attack. We found that anxiety level, as measured by the time that each individual spent in less-sheltered sectors (open arms of elevated plus-maze and center of open arena), was affected by both the social context and the gender of the tested individuals. While both female and male voles generally reduced their activity in the open following owl attack, males in mixed-gender groups were exceptional in dichotomizing into those that spent a short period and those that spent a long period in the open arms of the plus-maze. Based on the similar responses of the same-gender groups, we suggest that anxiety is contagious, and based on the lower anxiety level of the mixed-gender groups, we suggest that natural groups that comprise both males and females are better able to cope with life-threat compared with same-gender groups. Finally, we suggest that the differential responses of males in the mixed-gender groups were due to a few males that displayed a low level of anxiety. These males were probably individuals of high social rank, and their response reflects their natural protective role, as previously described in social voles.     

A field test of the Bruce effect in the monogamous prairie vole (Microtus ochrogaster)

The Bruce effect is a widely studied reproductive phenomenon in rodents in which exposure of pregnant females to unknown males causes termination of the current pregnancy. The Bruce effect has been reported from numerous studies in the laboratory, and one field study with the promiscuous gray-tailed vole, Microtus canicaudus, failed to support it. We conducted a field study with the monogamous prairie vole, M. ochrogaster, to determine if complete replacement of the male population every 10-14 days affected pregnancy and juvenile recruitment. The mean days to first parturition for control and treatment females were 36.8 and 44.4 days. Fifty-five percent of control females and 33% of treatment females conceived within the first 14 days of the study. All control females and 79% of treatment females successfully delivered at least one litter. These differences between treatment and control populations provide minimal support for the Bruce effect when compared with results from laboratory studies. Nulliparous females may have experienced some pregnancy disruption, but not parous females. Removal of mates, rather than exposure to strange males, may have contributed more to the lower reproductive success of treatment females than exposure to strange males. Treatment females, however, had lower juvenile recruitment than controls, which may have been due to infanticide from strange males. Our results are more similar to those of the field study of the gray-tailed vole than predicted, based on laboratory studies of prairie voles.     

The reproductive behavior and energetics of male gray seals (Halichoerus grypus) breeding on a land-fast ice substrate

The reproductive behavior of male gray seals (Halichoerus grypus) breeding on land-fast ice at Amet Island, Nova Scotia, was studied. Data on energy expenditure (rate of mass loss over time) were collected. The average time budget of males at Amet Island was comparable to that of land-breeding males. The behavior of males showed seasonal changes, with a decrease in the proportion of time spent in the water and an increase in agonistic behavior during the peak mating period. The estimated amount of body mass lost over the season ranged between 25.6 and 77.1 kg, and the estimated percent of initial body mass lost ranged between 7.7 and 26.5% (n=10). The maximum number of observed copulations for an individual male was nine. Only 15 out of 42 males observed during 1992 and 1993 were seen copulating. The number of observed copulations per male was strongly correlated with success in remaining close to, or attending, females (r=0.91, P<0.001, n=42). The mean duration of attendance was 4.5 ± 5.54 days (n=42). Large size was not an important factor in determining attendance success, but reproductive effort (the estimated proportion of body mass lost over the season) and success in agonistic interactions with other males were both correlated with male success.     

Infanticide by resident males and female counter-strategies in wild Japanese macaques (Macaca fuscata)

Infanticide was observed for the first time in a wild, non-provisioned troop of Japanese macaques on Yakushima Island, Japan. Eight adult resident males attacked unweaned infants in the pre- and early mating season, and one infanticide was observed directly. These attacks were not consistent with the social pathology, side effect of male aggression, cannibalism, or the resource defense hypothesis, but were generally consistent with the sexual-selection hypothesis. First, most male attackers had risen in dominance rank because several high-ranking males had left the troop. Second, in 78% of cases, male attackers had not previously been observed to mate with the mothers of victims. Moreover, analysis of subject animal DNA showed that males did not attack their own offspring. The two mothers who lost their unweaned infants, however, were not subsequently observed to mate. In fact, almost no mating behavior was observed in the troop. This was most likely due to a poor fruiting year. Resumption of mating by females who lost their infants may have been inhibited by an intervening environmental variable which suppressed female reproductive function. These observations contribute to a growing body of evidence which suggests that sexually selected infanticide can occur in seasonally breeding, multi-male, multi-female primate groups. Female Japanese macaques are known to mate with multiple males. We found evidence that female mating with multiple males inhibits contact aggression towards their infants. Adult males attacked infants eight times more often when they had not previously mated with the mother. Received: 2 September 1999 / Received in revised form: 27 April 2000 / Accepted: 3 May 2000     

Life history of Gonatus onyx (Cephalopoda: Teuthoidea): ontogenetic changes in habitat, behavior and physiology

In the present study 670 individuals of Gonatus onyx (Cephalopoda: Teuthoidea) were observed in Monterey Bay, California from a remotely operated vehicle. The vertical distribution of this species was bimodal, with peaks at 400 and 800 m depth during the day and 300 and 500 m during the night. The bimodal distribution reflects a life stage shift between younger, schooling juveniles living in shallower water and older, solitary adults which live deeper. Ontogenetic changes in behavior associated with this life stage shift are reflected in the physiology of the organisms as well. Both aerobic and anaerobic metabolism, as estimated using mitochondrial and glycolytic enzymes, decline with increasing body mass, suggesting reduced locomotory capacity in deeper-living adults. Oxygen consumption rates were also determined in relation to oxygen partial pressure. Oxygen consumption regulation was similar between juvenile and adult squids. The critical oxygen partial pressures (29 to 30 mmHg) correspond precisely to the oxygen concentrations found at the depth of maximal abundance for day and night populations of juveniles and adults, respectively. Behavioral and physiological changes with ontogeny of G. onyx are believed to result from reduced visual predator/prey interactions in the light-limited deep sea. Received: 7 February 1999 / Accepted: 26 January 2000     

Predicting the effects of habitat homogenization on marine biodiversity.

Seafloor habitats throughout the world's oceans are being homogenized by physical disturbance. Even though seafloor sediments are commonly considered to be simple and unstructured ecosystems, the negative impacts of habitat homogenization are widespread because resident organisms create much of their habitat's structure. We combine the insight gained from remote sensing of seafloor habitats with recently developed analytical techniques to estimate species richness and assess the potential for change with habitat homogenization. Using habitat-dependent species-area relationships we show that realistic scenarios of habitat homogenization predict biodiversity losses when biogenic habitats in soft sediments are homogenized. We develop a simple model that highlights the degree to which the reductions in the number of species and functional diversity are related to the distribution across habitats of habitat-specific and generalist species. Our results suggest that, by using habitat-dependent species-area relationships, we can better predict variation in biodiversity across seafloor landscapes and contribute to improved management and conservation.