Sexual size dimorphism,growth, and maturity of the fluvial eight-barbel loach in the Kako River,Japan

The maturation and growth pattern of the fluvial eight-barbel loach Lefua sp. (Japanese name: nagare-hotoke-dojo), an endangered species, was investigated using an individual identification-recapture method from 1995 to 1998 in an upper reach of a headwater tributary of the Kako River, Hyogo Prefecture, Japan. Based on observations of the gonads through the abdominal skin, the loach was estimated to breed mostly from May to July. All the males matured by age 1⁺, and all the females matured by age 2⁺. Gamete release in all individuals of both males and females was predicted from recaptured loaches during each breeding season. The standard length of mature females was significantly larger than that of males, showing sexual size dimorphism (SSD). The maximum sizes recorded were 75.4 mm SL for females and 61.2 mm SL for males. Both males and females of immature specimens grew mainly from May to November, including the breeding season, with no significant differences in growth rates between them. After sexual maturity, both males and females grew mainly from July to October (or November), after the breeding season, and the females exhibited higher growth rates than males. Therefore, SSD of the species seems to be attributable to the different growth rates after maturity. The longevity of the loach was estimated to exceed ten years based on individual growth patterns of various sizes during the survey period. It is likely that the loach has an iteroparous life history, breeding every year, and moderate growth rates after maturity.     

Variability of skull and dental characteristics in Mus spicilegus from the northern border of its distributional range

Results of morphometric analysis of the mound-building mouse (Mus spicilegus) evaluated in this study originate from field trapping in the eastern part of Slovakia during the years 2003–2008. Twenty-four cranial and dental variables and the zygomatic index (A/B) of 80 skulls (43 males, 37 females) were measured and evaluated with respect to the sex of the mice. Despite the fact that the overlap of skull measurements in adult males and females was high, sexual dimorphism was confirmed for several skull and dental traits. On average, the values for adult females of M. spicilegus were higher than males, with the exception of dental traits and the zygomatic index. Significant differences between adult males and females were found for the mean values of ten skull and dental parameters (LB, LCb, FL, LD, LMd, LaZ, LM¹, LM₁, LaM¹ and LaM₁). The values for the zygomatic index (A/B) overlapped between both sexes, but the higher average values in adult males were statistically significant. The results showed that the variability of the species confirmed in this paper was probably caused only at the regional level and did not differ from the findings reported by several authors for species from neighboring countries.     

Allometry of the postnatal cranial ontogeny and sexual dimorphism in Otaria byronia (Otariidae)

We studied the cranial postnatal ontogeny of Otaria byronia in order to detect sexual dimorphism in allometric terms, analyzing the rate of growth of functional variables linked to specific capacities as bite and head movements. We used 20 linear measurements to estimate allometric growth applying bivariate and multivariate analyses in females and males separately. Males were also analyzed in two partitioned subsets considering non-adult and adult stages, when the dimorphism is accentuated in order to reach optimal performance for intra-sexual competition. In the comparison of the employed techniques, we detected an empirical relationship between our multivariate results and the ordinary least square bivariate analysis. The quantitative analyses revealed different ontogenetic trajectories between non-adult and adult males in most variables, suggesting that the adult skull is not a scaled version of subadult skull. For instance, variables related with longitudinal dimensions decreased their allometric coefficients when the adult stage was reached, whereas those related with breadth or vertical dimensions increased their values. In adult males this could indicate that skull breadth and height are more important than longitudinal growth, relative to overall skull size. Conversely, inter-sexual comparisons showed that females and non-adult males shared similar ontogenetic growth trends, including more allometric trends than did males along their own ontogenetic trajectory. In general, adult males exhibited higher allometric coefficients than non-adult males in variables associated with bite and sexual behavior, whereas in comparison to females the latter showed higher coefficients values in these variables. Such patterns indicate a complex mode of growth in males beyond the growth extension, and are in partial agreement with changes previously reported for this and other species in the family Otariidae.     

Morphometics and Gonadal Development of the Hagfish Eptatretus cirrhatus in New Zealand

Hagfishes have been the target of commercial fisheries in many areas of the world, with the catch processed for leather and for human consumption. A fishery has been operating in New Zealand waters for the last six years, harvesting the bearded hagfish, Eptatretus cirrhatus. The fishery has thus far been unregulated. Based on samples collected dockside over a two-year period, this report expands the morphometric database for this species, provides information on the size and weight of the harvested animals, determines the sizes at the onset of gonadal development and the minimum sizes at sexual maturation for males and females, and indicates that E. cirrhatus, like most other hagfish species, has no specific breeding season. Although females appear in the population at smaller sizes, the sex ratio for mature animals is 1:1 and the sizes of the largest males and females are comparable. The changes observed in sex ratio as a function of TL suggest differences in the timing and rates of gonadal development in females versus males rather than protogyny. Based on the size of the eggs, the number of eggs per female, the proportion of the population that contains large eggs, and the number of postovulatory females, it is clear that E. cirrhatus, like other hagfish species, are potentially vulnerable to overexploitation.     

Testing Bergmann’s rule and the Rosenzweig hypothesis with craniometric studies of the South American sea lion

We tested the validity of Bergmann’s rule and Rosenzweig’s hypothesis through an analysis of the geographical variation of the skull size of Otaria flavescens along the entire distribution range of the species (except Brazil). We quantified the sizes of 606 adult South American sea lion skulls measured in seven localities of Peru, Chile, Uruguay, Argentina, and the Falkland/Malvinas Islands. Geographical and environmental variables included latitude, longitude, and monthly minimum, maximum, and mean air and ocean temperatures. We also included information on fish landings as a proxy for productivity. Males showed a positive relationship between condylobasal length (CBL) and latitude, and between CBL and the six temperature variables. By contrast, females showed a negative relationship between CBL and the same variables. Finally, female skull size showed a significant and positive correlation with fish landings, while males did not show any relationship with this variable. The body size of males conformed to Bergmann’s rule, with larger individuals found in southern localities of South America. Females followed the converse of Bergmann’s rule at the intraspecific level, but showed a positive relationship with the proxy for productivity, thus supporting Rosenzweig’s hypothesis. Differences in the factors that drive body size in females and males may be explained by their different life-history strategies. Our analyses demonstrate that latitude and temperature are not the only factors that explain spatial variation in body size: others such as food availability are also important for explaining the ecogeographical patterns found in O. flavescens.     

Nematodirus nemorhaedi sp. n. (Nematoda: Trichostrongylidae) from the Amur goral Nemorhaedus caudatus raddeanus]

Nematodirus nemorhaedi sp. n. is described. The new species was found in the small intestine in three long-tailed gorals from the Maritime Territory. The species differs from other species of the genus, parasites of ungulates, by very large (over 1.5 mm) spicules and characteristic structure of their distal end in males; by long (about 1 mm) ovijector in females and by a specific combination of characters of synloph, genital bursa in males, sizes of body, structure of vulva, sizes and shape of eggs and tail in females.     

Post-weaning maternal effects and the evolution of female dominance in the spotted hyena

Mammalian societies in which females dominate males are rare, and the factors favouring the evolution of female dominance have yet to be clearly identified. We propose a new hypothesis for the evolution of female dominance and test its predictions with empirical data from the spotted hyena (Crocuta crocuta), a well-studied species characterized by female dominance. We suggest that constraints imposed by the development of a feeding apparatus specialized for bone cracking, in combination with the intensive feeding competition characteristic of spotted hyenas, led to the evolution of female dominance. Specifically, we propose that protracted development of the feeding apparatus in young hyenas led to selection for increased aggressiveness in females as a compensatory mechanism for mothers to secure food access for their young after weaning. Our analyses yielded results consistent with this hypothesis. Morphological and behavioural measurements indicate that skull development is indeed protracted in this species; spotted hyenas do not achieve adult skull size or feeding performance capabilities until after sexual maturity. The period between weaning and completed skull development is particularly challenging, as indicated by high mortality. Finally, maternal presence between weaning and full skull maturity, as well as the relative ability of females to aggressively displace conspecifics from food, are important determinants of offspring survival.     

Protogynous hermaphroditism in the parrotfish,Calotomus japonicus

Sexual patterns of the parrotfish,Calotomus japonicus, were studied using fifteen specimens collected in February and April, 1990, near Makurazaki, Kagoshima Prefecture. The males ranged from 265 to 345 mm SL, and were larger than the females on average. Most females ranged from 202 to 260 mm SL, but a female of 305 mm SL was obtained. Sexual dichromatism was conspicuous. Histological examination of the gonads and low values of gonado-somatic indices of both males and females indicated that they were not in spawning season. It was concluded that C.japonicus is a protogynous hermaphrodite, because all male specimens had secondary testes. It was pointed out that the present species has a weak size-sex relationship. Because the specimens examined did not include primary males, it is suggested that primary males are relatively rare, if they occur at all.     

Bigger Is Not Always Better: Females Prefer Males of Mean Body Size in Philautus odontotarsus

Most species are believed to evolve larger body sizes over evolutionary time. Previous studies have suggested that sexual selection, through male-male competition and female choice, favors larger males. However, there is little evidence of selection against large size. The female serrate-legged small treefrogs (Philautus odontotarsus) must carry passive males from leks to breeding grounds over relatively long distances after amplexus to find a suitable place to lay eggs. The costs of large male size may therefore decrease mating success due to reduced agility and/or higher energy requirements. Thus, we hypothesized that selection would not favor larger males in P. odontotarsus. Females can assess male body size on the basis of the dominant frequency of male calls in frogs. To assess female P. odontotarsus preferences for a potential mate’s body size, male calls of high, average and low dominant frequency were played back to the females in phonotaxis experiments. Results showed that most females prefer the advertisement call with average dominant frequency. In addition, we compared the body mass distribution of amplectant males with that of single males in nature. The body masses of amplectant males are more narrowly distributed in the intermediate range than that of single males. The phonotaxis results and the data of actual female preferences in the field show that females strongly prefer potential mates of mean body sizes, consistent with the view that, in this species at least, larger males are not always perceived as better by females. In the present study, P. odontotarsus provides an example of an amphibian species in which large size does not have an advantage in mating success for males. Instead, our results provide evidences that stabilizing selection favors the optimal intermediate size of males.     

Does sexual experience affect the strength of male mate choice for high‐quality females in Drosophila melanogaster?

Although females are traditionally thought of as the choosy sex, there is increasing evidence in many species that males will preferentially court or mate with certain females over others when given a choice. In the fruit fly, Drosophila melanogaster, males discriminate between potential mating partners based on a number of female traits, including species, mating history, age, and condition. Interestingly, many of these male preferences are affected by the male''s previous sexual experiences, such that males increase courtship toward types of females that they have previously mated with and decrease courtship toward types of females that have previously rejected them. D. melanogaster males also show courtship and mating preferences for larger females over smaller females, likely because larger females have higher fecundity. It is unknown, however, whether this preference shows behavioral plasticity based on the male''s sexual history as we see for other male preferences. Here, we manipulate the sexual experience of D. melanogaster males and test whether this manipulation has any effect on the strength of male mate choice for large females. We find that sexually inexperienced males have a robust courtship preference for large females that is unaffected by previous experience mating with, or being rejected by, females of differing sizes. Given that female body size is one of the most common targets of male mate choice across insect species, our experiments with D. melanogaster may provide insight into how these preferences develop and evolve.     

Age variability of the sexual size dimorphism in sables in nature and captivity

Inter-sexual differences in craniometric parameters were studied in sables of varying sex and age in natural (n = 2338) and farm (n = 516) populations. In nature, the differences between the skull size in males and females are, as a rule, highly significant (p < 0.001) and the size dynamics correlate well with age. In the farm population, the difference in the skull size between the sexes is statistically significant (p < 0.01), but the correlation of sizes with age is absent. In natural populations, index of sexual dimorphism (ISD) correlate positively with age, with a maximum correlation found in the animals aged nine and a minimum found in juveniles. The index of sexual dimorphism grows considerably until three years of age, after which the dynamics resemble a cyclical process with a repetition of maximum values each fourth year with a general trend of growth in the ISD. The highest values of ISD in farm sables are registered at 3?C5 years of age, while the minimum ones are noted in the age groups of 6?C9 and 13?C14 years of age. In nature, juveniles aged 6?C10 months are characterized by a tendency to general growth (which is not manifested in the introduced population from the basin of the Vakh River) and increase in the SD index with age. The Vakh population is characterized by a decrease in the SD index. The specific rate of skull growth in males is 1.8-fold higher than in females. The age dynamics of the skull size and the vectors of rates between the sexes are not in accordance, as a rule. The results of our study correspond to the theory by Geodakyan (1991) about dichronomorphism. In our opinion, the differences in age manifestations of sexual dimorphism and postnatal skull growth in natural and farm sable populations are determined by the different directions of selection.     

Female Size Influences Mate Preferences of Male Guppies

Guppies (Poecilia reticulata) have a promiscuous mating system in which female choice for brightly coloured males plays an important role. Consequently, much research on guppies has examined how mate choice by females has lead to the evolution of male colour patterns. Much less attention has been devoted to mate choice by males in this species. In this study, we show that male guppies are choosy when selecting a female to associate with, significantly preferring the larger female when presented with two females that differed by ≥2 mm in standard length (SL). The strength of their preference for each female increased with absolute female size. The relative sizes of the females, however, also influenced male mating preferences: males showed stronger preferences for the larger female as the difference in SL between the two females increased. Such a preference for larger females is not unexpected as fecundity generally increases with body size in female fish. Thus, males choosing to mate with the larger female should have higher reproductive success. An apparent, but non‐significant anomaly, whereby males appear to prefer the smaller of the two females when the difference between female SL was <4 mm, deserves further investigation.     

Aspects of reproduction and their implications for the conservation of the endangered limpet,Patella ferruginea

Summary

The protandric limpet, Patella ferruginea G., is the most endangered marine species in the Western Mediterranean and is at serious risk of extinction. Nevertheless, its biology and ecology are little known. In the present work, several reproductive aspects are studied. Recruitment take place in June and the largest individuals are the most scarce. The sex ratio is slanted towards the largest sizes, and the species seems to show sex change at sizes from 60 mm upwards, although males can be observed up to 80 mm. There is no correlation between size of oocytes and shell length; however, the larger females contribute greatly to the reproductive event, with high fecundity and GSI values. The mean diameter of oocytes was observed to be 149.78 μm, whereas the heads of spermatozoa were 3.78 μm long. The results of the present study increase the maximum length for males by double that cited in previous literature and highlight the importance of strictly protecting females (i.e., most of the largest individuals, >60 mm), since their population percentage is very low, in order to develop adequate strategies to preserve the species.     

Age, growth, reproduction and mortality of the striped seabream, Lithognathus mormyrus (Pisces, Sparidae), off the Canary Islands (Central-east Atlantic)

Striped seabream, Lithognathus mormyrus L. (n=731) caught off the Canary Islands from January 1999 to June 2000 were studied. Fish ranged in size from 113 to 372 mm total length, weighing from 21.1 to 748.2 g total weight. Weight increased allometrically with size (b=2.9071). Fish age was 0–10-years-old. Growth was relatively slow (k=0.88 years⁻¹), with females growing at a slightly faster rate than males. The species displayed protandric hermaphroditism. Male : female ratio was unbalanced in favour of males (1 : 0.85). Males predominated in smaller sizes, females in larger sizes, and intersexual individuals were in intermediate sizes. The reproductive season extended from June to December, with a peak in spawning activity in August–September. Males reached maturity at 207 mm (2 years) and females at 246 mm (3 years). The real value of instantaneous rate of natural mortality was between 0.30 and 0.45 years⁻¹.     

Use of space by Necromys lasiurus (Rodentia,Sigmodontinae) in a grassland among Atlantic Forest fragments

The spatial patterns presented by the rodent Necromys lasiurus were studied through capture-mark-recapture in a grassland among Atlantic Coastal Forest fragments in Southeastern Brazil. Males moved farther than females. Males moved similar distances in the dry and wet seasons, whereas females moved significantly longer distances in the dry season. Home ranges sizes were estimated for 32 individuals, and varied from 0.02 to 0.52 ha. Males had larger home ranges than females when all data are pooled and in the wet season; in the dry season home ranges of both sexes were of similar sizes. Home range sizes did not vary significantly between seasons for either sex. Home ranges of males overlapped extensively among themselves and with females, whereas females showed mutually exclusive home ranges. The spatial patterns described here are consistent with the results found for this species in different habitats and they suggest that N. lasiurus has a promiscuous mating system.     

Body size and craniometry of the herb field mouse from Lithuania in the context of species range

We present morphometric and craniometric measurements of the herb field mouse (Apodemus uralensis) from Lithuania and analyze variation of body and skull size across species range. We suppose species is characterized by high size variability, not following Bergmann’s or Murphy’s rules. Preliminary, distinct size differences have been registered in the eastern and southern edges of the distribution range, with these populations having largest individuals according to average body and skull size. In terms of tail length and condylobasal length of the skull, Lithuanian mice on the north-western edge of the species range are among the largest, but in terms of body weight, body length, zygomatic skull width and the length of maxillary toothrow, adult A. uralensis from Lithuania are small and correspond to those from populations on the western edge of the range. The relative skull width (ratio of zygomatic skull width to condylobasal length) of Lithuanian A. uralensis is the smallest across the entire range. In A. uralensis from Lithuania, sex dimorphism is weakly expressed, with hind foot length and postorbital constriction larger in adult males, while the height of the mandibula and length of the mandibular diastema is larger in adult females. Juvenile and subadult A. uralensis from Lithuania differ in body weight, but not in size.     

Testing predictions for the evolution of lekking in the sandfly, Lutzomyia longipalpis

We carried out a combination of field and laboratory experiments to investigate two possible mechanisms promoting the evolution of lekking in the sandfly, Lutzomyia longipalpis. Males in this species lek on or near hosts that females visit to mate and feed. To test whether the distribution of resources, lek size and female number were positively correlated (a prediction of hotspot models) we manipulated the availability of potential lek sites by varying the numbers of chickens, Gallus gallus domesticus, held in field cages. We then investigated the distribution of males and females across leks formed within these cages and measured males to assess the relationship between male size and lek size. The number of males attracted to a lek increased with the number of hosts present and on average males on larger leks had longer abdomens. The number of females was positively correlated with the number of males present, but the average number of females per male decreased with increasing lek size. In a second experiment, we introduced single females to laboratory leks of different sizes, and compared female latency to mate. Contrary to an explicit prediction of the black hole model, lek size had a direct effect on a female's latency to mate. Females at larger leks encountered and copulated with males sooner than those at smaller aggregations, but the length of time a pair spent courting did not vary with lek size. Our results suggest that the black hole model is unlikely to explain the evolution of lekking in this species. The data instead support the hotspot model as a possible mechanism promoting lekking in L. longipalpis but suggest that female preference for larger leks may need to be invoked to obtain the degree of aggregation observed.     

Factors limiting polygyny in the willow ptarmigan

Willow ptarmigan (Lagopus lagopus) usually pair monogamously and males invest more in vigilance and parental care than do males of other grouse species. I tested whether polygyny is rare because male parental care is necessary for successful reproduction. By continuous removal of males I skewed the operational sex ratio, induced polygyny, and then compared breeding success and survival of females that shared a mate and those that did not. Both groups had similar clutch sizes, laid eggs at the same time, produced young of the same weight, and fledged similar numbers of juveniles. Hens that shared a mate suffered higher losses of nests during incubation, and fewer returned to the breeding range in subsequent years. Thus, although male parental care was not essential, it did improve female reproductive success and survival. I suggest that willow ptarmigan are not polygynous because territorial females are able to prevent potential secondary hens from settling, thus securing unshared access to male investment and territorial resources.     

Effects of female and male size on female mating and remating decisions in a bean beetle

The body sizes of individuals of the choosing and chosen sexes in a mate choice may affect sequential mating of females. We examined the effects of the body sizes of females and their mates on attributes of female first mating, and the effects of body sizes of females and their previous and potential future mates on female remating in the adzuki bean beetle, Callosobruchus chinensis. Large- and small-sized adults were derived from larvae reared under conditions of low and high density in a bean, respectively. The speed of first mating of large females was not affected by the size of courting males, whereas small females initiated mating more rapidly when courted by small males. The remating probability of large females was not affected by first male size, whereas small females that mated first with smaller males were more likely to remate. These data suggest that pre- and post-copulatory female choices for male size depend on the female’s size, and the small females might be more willing to copulate with smaller males but prefer larger males to sire their offspring after copulation. A possible explanation for this preference is that small females may suffer greater harm from copulating with larger males.     

Intraspecific shape variation in horseshoe crabs: The importance of sexual and natural selection for local adaptation

A morphometric analysis of the body shape of three species of horseshoe crabs was undertaken in order to infer the importance of natural and sexual selection. It was expected that natural selection would be most intense, leading to highest regional differentiation, in the American species Limulus polyphemus, which has the largest climatic differences between different populations. Local adaptation driven by sexual selection was expected in males but not females because horseshoe crab mating behaviour leads to competition between males, but not between females. Three hundred fifty-nine horseshoe crabs from nine populations, representing three species, were analyzed using a digitizer to position sixty morphometric landmarks in a three-dimensional space. Discriminant analysis revealed strong regional structuring within a species, which suggests strong philopatry, and showed the existence of geographically-based intraspecific variation. An admixture analysis showed regional intraspecific differentiation for males and females of L. polyphemus and males of the Asian horseshoe crab Carcinoscorpius rotundicauda, but not for females of C. rotundicauda and another Asian horseshoe crab, Tachypleus gigas. Differences in shape variation between sexes were tested with F-tests, which showed lower intrapopulation morphometric variation in males than females. These results indicate a lower degree of local adaptation on body shape in C. rotundicauda and T. gigas than in L. polyphemus and a lower degree of local adaptation in females than in males.