Sex Differences In Size Research Articles

Variation of eye size in butterflies: inter- and intraspecific patterns

Differences in behaviour, such as the mate-locating tactic, may favour the evolution of interspecific and intersexual differences in the structure of the visual system. This notion was tested by examining the relationships between eye size, body size, sex and mate-locating tactic in 16 species of butterflies. The 16 species were grouped in eight phylogenetically close pairs that differed in the mate-locating tactic displayed by the males. Eye size was characterized by eye surface area, which was estimated from a set of linear eye measurements made on 10 individuals of each sex in each species. The major findings were that eye surface area was positively correlated with body size both among and within species, males have larger eyes relative to their body size than females, and after controlling for body size and phylogeny, interspecific differences in the mate-locating tactic of males does not explain interspecific variation in the size of male eyes or in the magnitude of sexual difference in eye size. The optical and behavioural consequences of variation in eye size with body size and sex will await a better understanding of how eye structure varies with size within and between species.

Rib remodeling dynamics in a skeletal population from Kulubnarti, Nubia.

Bone remodeling variables in the rib were analyzed for a skeletal population of medieval antiquity (ca. A.D. 550-1450) from Kulubnarti, in Sudanese Nubia. The skeletal remains are naturally mummified and in an excellent state of preservation. The study sample consists of thin sections from the ribs of 80 individuals, ranging in age from 15-50+ years. Ribs were examined using a standard microscope and image analysis software. Numbers of intact osteons, fragmentary osteons, forming osteons, and resorption spaces were counted, osteon and Haversian canal areas were measured, and several variables were calculated to assess morphometric and remodeling status in the rib. Variables calculated included mean annual activation frequency, mean bone formation rate, and net osteonal remodeling. Results indicate that age changes are consistent with those observed for other archaeological and modern samples. High numbers of resorption spaces in young males may reflect slower skeletal development in boys compared to girls. Comparisons of rib data with results of a previous study on patterns of femoral bone remodeling in the same population indicate that ribs have more osteons and higher bone formation rates compared to the femur. Also, sexual differences in osteon size observed in the femur were not observed in the rib. Activation frequency and bone formation rate are low in the Kulubnarti population compared to previously published data for a modern sample, a finding consistent with reported results from other archaeological samples. Genetic factors influencing the minimum effective strain setpoint and duration of skeletal maturation, in addition to repetitive high strains at Kulubnarti, may contribute to observed differences.

Sex Differences in Proximal Humeral Outline Shape: Elliptical Fourier Functions

A method is presented for the numerical analysis of sex differences in size and shape of the proximal humeral outlines using elliptical Fourier functions (EFFs). A skeletal sample consisting of right and left humeri pairs of 69 individuals, 36 males and 33 females, was used. The proximal superior view in the plane of the proximo-distal axis of each humerus was photographed and then 54 boundary points were located on the two-dimensional outline tracings. These points were digitized and used to compute EFFs with 27 harmonics. From the EFFs, a set of expected points on the proximal humeral outline was generated using the centroid as an origin. Superimposition of the male and female outlines on this centroid provided a detailed picture of the relative sex differences in size and shape with respect to that center. The bounded area of the proximal humeral outline showed statistically significant sex differences. Additionally, statistical results of the amplitudes derived from the "area-standardized" EFFs and visual assessments of the mean outline plots indicated significant sex differences in shape of the proximal humeral outlines. Focusing on localized regional differences, the greater tubercle was located more postero-medially and the lesser tubercle was located more anteriorly in the males compared to the females. Sex determinations from the proximal humeri were also examined with discriminant functions based on the amplitudes, which represent shape characteristics of the outline, and the hounded area. Using a cross-validation method, predictions of the percentages of cases correctly classified with the discriminant functions were ranged from 92.8% to 95.7% for the right and left humeral data. These results suggest that differences in size and shape of the proximal humeral outlines may be better predictors of sex when compared with conventional measurements of the humerus.

Sex differences in dog corpus callosum.

Human studies reported sex differences in size and shape of the corpus callosum. These observations have been contested. The purpose of the present study is to investigate possible sex differences in the corpus callosum of dogs. The entire brains including the medulla from 12 female and 9 male adult mongrel dogs were removed and weighed. Total and partial area measurements of the callosum were made from photographic tracings of its outline. The callosum was partitioned into 3 regions; anterior half, posterior half, posterior one-fifth. The total corpus callosum, anterior half, posterior half, and posterior fifth or splenium areas were measured. Sex differences were found. The anterior half, the posterior half, the posterior fifth, and the total callosum were significantly greater in absolute area in males than in females.

Paedogenesis in European newts (Triturus: Salamandridae): Cranial morphology during ontogeny

ABSTRACT A cross-sectional analysis using different ontogenetic stages (larvae, juveniles, paedotypic, and metamorphic adults) of the smooth newt, Triturus vulgaris, and the alpine newt, T.alpestris, revealed a broad spectrum of perennibranchiation influences on cranial ontogeny in European newts, more pronounced than previously thought. These influences included marked variation in ossification levels, pronounced morphometric variability of many cranial elements, and considerable skull shape changes in the transition from larvae to the adult stage. In comparison with metamorphosed individuals, paedotypic newts had a higher level of variability in both individual cranial traits and cranial shape changes. Sexual size difference of the skull traits was mostly negligible, especially in comparison to the influence of paedogenesis. The main changes in cranial shape of the European newts occurred during metamorphosis. Cranial morphological organization in the majority of examined paedotypes corresponds to cranial organization at late larval stages prior to metamorphosis or at the onset of metamorphosis. J. Morphol. 243:127–139, 2000 © 2000 Wiley-Liss, Inc.

Paedogenesis in European newts (Triturus: Salamandridae): Cranial morphology during ontogeny

A cross-sectional analysis using different ontogenetic stages (larvae, juveniles, paedotypic, and metamorphic adults) of the smooth newt, Triturus vulgaris, and the alpine newt, T.alpestris, revealed a broad spectrum of perennibranchiation influences on cranial ontogeny in European newts, more pronounced than previously thought. These influences included marked variation in ossification levels, pronounced morphometric variability of many cranial elements, and considerable skull shape changes in the transition from larvae to the adult stage. In comparison with metamorphosed individuals, paedotypic newts had a higher level of variability in both individual cranial traits and cranial shape changes. Sexual size difference of the skull traits was mostly negligible, especially in comparison to the influence of paedogenesis. The main changes in cranial shape of the European newts occurred during metamorphosis. Cranial morphological organization in the majority of examined paedotypes corresponds to cranial organization at late larval stages prior to metamorphosis or at the onset of metamorphosis.

Copulatory Sequences and Sexual Struggles in Millipedes

Behavioral sequences were followed in the millipede genus Centrobolus (Diplopoda: Spirobolida: Pachybolidae). Precopulatory struggles included a combination of female coiling, the antipredator response, and male coercion and uncoiling. During copulation three male behaviors were always performed—antennating, glandular secretion and sexual collaring—all three were candidates for cryptic female choice. In species with highly prolonged copulation (e.g., Centrobolus inscriptus, 170.0 ± 49.3 min), the male coiled around the female and produced a large “sexual collar,” defined upon timely hydraulic movements in the region of genital contact. In species with shorter copulation (e.g., C. ruber, 39.8 ± 13.2 min), the pair copulated in parallel and lacked the sexual collar. Variance in copulation duration produced significant trends, e.g., female size correlated with the prolonging of copulation duration, and there were indications of a conflict of sexual interests for controlling when copulation would be terminated. Stand-by males that were unsuccessful at take-over accompanied copulatory triplets and clusters of mating pairs. Polygynandrous mating systems of these millipedes incorporate diametric pressures on males to maximize copulation numbers and duration, and females to perform endurance rivalry based upon sexual size differences. This study provides a useful comparison for insects where copulation is also prolonged.

Predicting home range size from the body mass or population densities of feral pigs, Sus scrofa (Artiodactyla: Suidae)

AbstractTelemetry studies of feral pigs (Sus scrofa, L.) in different habitats were used to predict home range size, from (i) body mass and (ii) population density. Geometric mean regressions of the loge transformed data indicated that body mass of male and female feral pigs and mean population density were good predictors of the home range size of feral pigs (r2 = 0.81, 0.77 and 0.85 respectively). There were no sexual differences in home range size of feral pigs once the effect of body mass was taken into account. Use of these variables in models that incorporate spatial aspects along with the practical application of the results to the management of feral pig populations are briefly discussed.

Pectoral fin size in a fish species with paternal care: a condition‐dependent sexual trait revealing infection status

Summary1. The three‐spined stickleback, Gasterosteus aculeatus L., is a territorial fish with exclusive male parental care. Males oxygenate the eggs with fanning movements of their pectoral fins. The present authors investigated whether the apparent sexual differences in the functional demands of the pectoral fins have resulted in sexual differences in fin size. If males have relatively larger pectoral fins, females may use this as a signal to aid their mate choice for good fathers. Therefore, further objectives were to study the condition‐dependency of relative pectoral fin size in males and the relationship with male parasite load.2. Reproductively active males possessed relatively larger pectoral fins than females in both wild‐caught and laboratory‐bred fish.3. In the field, caring males with relatively large pectoral fins were in better physical condition and had more food in their stomachs.4. Relatively small pectoral fins and poor body condition were associated with infection by the intestinal parasite Pomphorhynchus laevis (Acanthocephala), the prevalent parasite species in the study population.

Problems Encountered When Banding Frigatebirds and Boobies

-Two problems were encountered when banding frigatebirds (Fregata spp.) and boobies (Sula spp.). These are related to 1) the age at which chicks are banded and 2) size differences in adults. The problems, not addressed in the North American Bird Banding guidelines published jointly by the U. S. Fish and Wildlife Service and Canadian Wildlife Service (USFWS, 1991), include guano buildup inside the bands of downy frigatebird chicks and geographical and sexual size differences in adult birds of both genera. Both problems can cause deformities in the foot and leg of banded birds. I discuss correct procedures for banding these species and urge the development of longer lasting, non-corrosive, and easy to apply bands for long-lived birds. Received 10 March 1999, accepted 7June 1999.

Growth of dark chub, Zacco temmincki (Cyprinidae), with a discussion of sexual size differences

Growth of dark chub, Zacco temmincki (Cyprinidae), with a discussion of sexual size differences

Daylength and Temperature Control of Predation, Body Size, and Rate of Increase in Toxorhynchites rutilus (Diptera: Culicidae)

Subtropical Toxorhynchites rutilus (Coquillett) frequently overwinter as 4th instars in treeholes of peninsular Florida. Exposure from hatch to short daylengths induced 4th instar diapause in over 50% of wild T. rutilus from southern Florida. Short daylengths and lower temperatures significantly reduced prey consumption rates. At a low frequency, diapausing larvae killed prey without consuming, which behavior increased with time in the 4th instar and was distinct from killing by prepupae. Termination of diapause by transfer of 4th instars to long daylengths was accompanied by an increase in prey consumption rate prior to pupation. Mean pupal masses were significantly affected by photoperiod and temperature treatments, confirming a correlation between heavier pupae and colder temperatures in the field. At 25°C and 21°C, female pupae were significantly larger than males, in contrast to no sexual size difference observed for continuous development at 27°C. The composite index of performance (r’), an analog of the per capita rate of increase, for diapausing cohorts was one-half to two-thirds of that estimated for non-diapausing cohorts, but temperature alone did not affect r’ between 25 and 21°C. Low rates of prey consumption during winter diapause may contribute to the relatively modest, albeit significant, effect of T. rutilus predation on mosquito abundance as estimated from long-term censuses of treeholes.

Sex Difference in the Size of the Neural Song Control Regions in a Dueting Songbird with Similar Song Repertoire Size of Males and Females

Previous studies have suggested a causal relation between sex differences in behavior such as singing and sex differences in the size of brain areas such as the forebrain song control areas of songbirds. In the present study we show that the size of the forebrain vocal control areas nucleus hyperstriatalis ventrale pars caudale (HVC) and nucleus robustus archistriatalis (RA) and its neuron numbers are about twice as large in males as in females of the African dueting bush shrike Laniarius funebris. However, song types are of similar complexity (number of elements per song type, physical properties of elements) in both sexes, and repertoire size does not differ between males and females. Furthermore, in captivity male and female shrikes are able to learn the same song types. This demonstrates for the shrike that sex differences in the size of vocal control areas and in its neuron numbers do not predict the type of sex-typical vocal behavior. This result is supported by a statistical comparison of the sex differences in HVC size, RA size, and song repertoire size of all songbird species studied to date. Sex differences in species in which only the males sing are indeed larger than in species in which the females also sing; in songbird species with singing females, however, the sex differences in HVC and RA volume appear to be independent of the vocal repertoire size of females. The songbird model therefore does not support the notion that sex differences in area size and neuron number explain sex differences in a behavior that occurs in both sexes. Furthermore, in the shrike, neuron soma size is similar in males and females in the song motonucleus hypoglossus pars tracheosyringealis (nXIIts) and in the premotor nucleus RA, but is sexually dimorphic in the higher vocal center HVC. Thus, male and female shrikes produce songs of similar complexity with different neuron phenotypes.

Extreme Sexual Size Dimorphism, Sexual Selection, and the Foraging Ecology of Montezuma Oropendolas

Sexual differences in body size usually are considered to be a product of either sexual selection or ecological divergence between the sexes. I tested the predictions of these hypotheses to explain extreme sexual dimorphism in size in a Neotropical blackbird, the Montezuma Oropendola (Psarocolius montezuma). Sexual dimorphism was more pronounced in wing length and relative mass, traits that appear to be important in courtship and competition for mates, than in bill length or tarsus length. Male dominance rank, which is an indicator of mating success, was positively associated with body size (i.e. high-ranking males were larger than low- ranking males). These results suggest that sexual selection acts to increase male body size, and hence contributes to sexual size dimorphism in this species. Differences in foraging behavior and diet also existed between the sexes and were related to sexual size differences. The small size of females allowed them to forage on food resources that were difficult for the larger males to reach (e.g. insects in rolled leaves at the ends of branches). Females, though, did not appear to be restricted from those resources exploited by males (primarily epiphytal bromeliads). Although it was not possible to reject the ecological- divergence hypothesis, my results suggest that sexual foraging differences are a consequence rather than a cause of sexual dimorphism in size in this species.

Sexual, Seasonal and Group Size Differences in the Allocation of Time between Vigilance and Feeding in the Greater Rhea, Rhea americana

AbstractWe studied the effect of sex and group size on the proportion of time a greater rhea, Rhea americana, allocates to vigilance and feeding during the breeding and the non‐breeding seasons. We analysed 175 records of focal animals that were feeding alone or in groups of 2 to 26 birds. In both seasons, males spent more time in vigilance and less time in feeding than females. Both sexes spent more time in vigilance and less time in feeding during the breeding season. Sexual and seasonal differences in vigilance were the result of different mechanisms. Males had shorter feeding bouts than females but there were no sexual differences in the length of the vigilance bouts. On the contrary, seasonal differences were the result of males and females having longer vigilance bouts during the breeding season but there were no seasonal differences in the length of the feeding bouts. During the non‐breeding season, individual vigilance was higher in rheas foraging alone than in groups. In this case, solitary birds had longer vigilance and shorter feeding bouts than birds foraging in groups. We discuss the possible effect of intragroup competition and food availability on the allocation of time between feeding and vigilance in this species.

Nucleolar size and shape is sexually dimorphic in neurons of the lateral magnocellular nucleus of the anterior neostriatum (LMAN) in birds.

The lateral magnocellular nucleus of the anterior neostriatum (LMAN) in birds plays an important role in songlearning processes. Recently, it has been shown that structural changes at the cellular level in males are causally related to vocal learning. Whereas males sing, females do not. This sexual difference in behavior is also reflected in sexual differences in the neuronal structure in adult birds, with males having larger neuronal somata than do females. In the present report, the size and shape of the nucleoli were investigated to determine if sexual differences were also present at the nucleolar level. The data demonstrated a strong sexual difference in nucleolar size in both juvenile and adult birds, the cross-sectional area of the nucleoli being significantly larger in males than in females (30% and 50% larger in juvenile and adult birds, respectively). This difference between males and female finches was also reflected by the cross-sectional area of a specific type of nucleolus exhibiting a central light area. In both sexes, nucleoli exhibiting a central light area were significantly larger in juvenile and adult birds than nucleoli that lacked a central light area. The percentage of neurons exhibiting a central light area was higher in adult males than in adult females, but not in juvenile birds. The time course of development of nucleoli exhibiting a central light area in males was very similar to the development of neuronal somata size in LMAN neurons. The larger size of the nucleoli in LMAN neurons in males and the developmental changes in the incidence of nucleoli exhibiting a central light area may be indicative of a high level of ribosome production necessary for song-learning processes to occur.

No sex difference occurs in hippocampus, food-storing, or memory for food caches in black-capped chickadees

A number of recent studies have described sex differences in the relative size of the hippocampus that are associated with sex differences in the use of space. Voles, kangaroo rats, and cowbirds all exhibit a sex difference in relative size of the hippocampal formation that is correlated with a sex difference in spatial behaviour. We wished to determine whether sex differences in the size of the hippocampus occur in the absence of a difference in the use of space, and whether the previously described correlations could be adventitious. Relative hippocampal size was determined in wild-caught black-capped chickadees ( Parus atricapillus) following behavioural observations of food caching and spatial memory for cache sites. There was no indication of a sex difference in either relative size of the hippocampus or in food-caching behaviour and memory for cache sites. These results show that sex differences in relative size of the hippocampus do not occur as a matter of course, and are consistent with the hypothesis that sex differences in spatial behaviour and spatial ability are predictive of sex differences in the relative size of the hippocampus.

Size and scaling of sexually‐selected traits in the lizard,Uta palmeri

Differences between the sexes in overall body size and in the size of other morphological traits, relative to overall body size, are common in many animals. In this study, patterns of growth and scaling of sexually dimorphic tratis are assessedin a lilzard and then used to sugest general developmental mechanisms responsible for sexual size dimorphism (SSD). Adult makeUta palmerilizards are larger than adult females inoverall body size (snout‐vent length, SVL), body mass, jaw length head width, and head depth. Two general growth processes produce this adult SSD. First, juvenile males have greater annual SVL growth rates than do juvenile females, contributing to adult SSD because males will be larger than females in any trait positively correlated with SVL. Secondly, males and females differ in age‐related changes in growth of the three head size traits, relative to growth in SVL. Comparing slopes from reduced major axis regressions of each trait on SVL reveals that the sexes do not differ in the scaling of these traits as juveniles, but as adults males have greater slopes than adult females, indicating ontogenetic differences in scaling of these traits in males. Two other topics in SSD are addressed with these data. First, comparing these data on scaling to those of an earlier analysis that used ordinary least squares regression reveals that conclusions about underlying mechanisms in an analysis of scaling can be altered by the choice of a regression model. Secondly, these data indicate that postmaturational differences in scaling contribute to adult sexual size differences, contrary to an earlier study. Shine (1990) found that for many ectotherms, which continue to grow after sexual maturation, post‐maturational events contribute little to sexual differences in overall body size. Results forU. palmerisuggest that these findings may only hold for measures of overall body size (e.g. SVL) and may not generalize to traits that exhibit sex difference in scaling.

Geographical ecology of a Neotropical lizard: Ameiva ameiva (Teiidae) in Brazil

The large-bodied teiid lizard Ameiva ameiva was studied at eight different sites in four major South American habitats of Brazil: caatinga, cerrado, Amazonian rain forest, and Amazonian savanna. We found striking similarity in ecological attributes of this lizard among very different habitats. Activity is concentrated in late morning and early afternoon; active body temperatures average 37.9 ± 0.09 °C and vary little among sites or throughout the day; the diet consists of a variety of vertebrates and invertebrates but is dominated by grasshoppers, roaches, beetles, spiders, and insect larvae; and niche breadths for prey are similar among study sites but the actual composition of the diets varies. There is minimal morphological variation among sites (mostly size); the most striking morphological variation is between the sexes. Males reach larger body sizes and have relatively larger heads than females. Juveniles have relatively larger heads than would be predicted on the basis of body size alone. Sexual selection may explain the sexual differences in head size of adults, whereas the relatively large heads of juveniles may be associated with food competition with sympatric teiid lizards. Clutch size varies from 1 to 11 eggs, is related to female body size (snout–vent length), and varied among study sites. Similar variation among sites occurs in egg size but not in relative clutch mass. An interesting positive relationship was found between body size and relative clutch mass. In a population from the state of Rondônia egg dry mass was correlated with female size, indicating that individual offspring size is, to some extent, a consequence of female size. The reproductive season is extended for all populations and it appears that predictability of rainfall may regulate the season length. Reasons for the apparent success of A. ameiva in a diversity of habitats on a large geographic scale include its large body size, foraging mode, and preferred microhabitat (ecotones and disturbed areas).

Horsehair Worms (Phylum Nematomorpha) in Wisconsin, With Notes on Their Occurrence in the Great Lakes

ABSTRACT Wisconsin records for Chordodes morgani, Gordius robustus, and Paragordius varius are summarized. The occurrence of horsehair worms in the Great Lakes Is reviewed. Sexual size differences are demonstrated In G. robustus, with females being significantly longer than males. Skewing of sex ratios in horsehair worm populations is discussed.