Mean Size Of Females Research Articles

Testing ecological and developmental hypotheses of mean and variation in adult size in nephilid orb-weaving spiders

Fecundity selection has been hypothesized to drive the evolution of female gigantism in the orb-weaving family Nephilidae. Several species of these spiders also exhibit large amounts of variation in size at maturity in one or both sexes. In this article, we attempt to detect correlations of mean and variation in adult size at a phylogenetic scale between the sexes and with latitude. We tested six predictions derived from three broad developmental, ecological, and age structure hypotheses, using independent contrasts and a recent species-level nephilid phylogeny as well as least squares and other conventional statistics: 1. In both sexes, species with larger mean size will have greater variation in size; 2. Males and females will show correlated changes in mean size and of variation in size; 3. In both sexes, mean size will be negatively correlated with the midpoint of the latitudinal range; 4. In both sexes, tropical species will be more variable; 5. In both sexes, more widespread species will be more variable; 6. Variation in male size will be positively correlated with mean female size. In no cases were male and female development correlated, suggesting that in this lineage male and female body size evolve independently. The only significant trend detected was a positive phylogenetic correlation between variation in female size and latitude, the opposite of prediction 4. Power tests showed that in all tests of the ecological hypothesis, sample sizes were more than adequate to detect significant trends, if present. Our results suggest that evolutionary trends in juvenile development among species are too weak to be detectable in such data sets.

Reproductive plasticity in Petrolisthes armatus (Anomura, Porcellanidae): a comparison between a Pacific and an Atlantic population

The porcellanid crab Petrolisthes armatus, with a known geographic distribution covering a wide range of latitudes, was selected to conduct a comparative study on egg production and reproductive output between two populations from Pacific and Atlantic coasts. Ovigerous females were collected between September and November 2005 in Punta Morales, Pacific coast of Costa Rica (n = 137) and from March 2005 to July 2006 in Araca region, Sao Paulo, Brazil (n = 46). The mean size of females was statistically different between both populations with larger females from Brazil than Costa Rica (7.9 ± 1.31 and 6.6 ± 0.95 mm CW, respectively). Likewise, egg production was significantly different in both populations and started in Pacific Costa Rica at a smaller female size than in Brazil. Specimens from Pacific Costa Rica produced roughly three times more eggs than equally sized females from Brazil, while newly extruded embryos were larger in Brazil than in Costa Rica (0.045 and 0.039 mm3, respectively). Egg volume increased during embryogenesis by 112.8 and 164.5% in Costa Rican and Brazilian populations, respectively. The egg water content increased steadily in both populations; however, eggs produced in Brazil contained always more water than those from the same developmental stage in Costa Rica. Average reproductive output (based on dry weight) was substantially lower in Brazil (0.031) than in Costa Rica (0.065). Our results confirm an impressive intraspecific plasticity of reproductive features in an intertidal decapod. The observed phenotypical variability might be related to local environmental conditions as well as to the location of the studied population concerning its geographic range of distribution.

Environmental and fishing effects on the abundance, size and sex ratio of the blue‐throated wrasse, Notolabrus tetricus, on South Australian coastal reefs

Abstract The blue‐throated wrasse, Notolabrus tetricus (Richardson), is a site‐attached protogynous hermaphroditic species, with a small home range of 1000–2000 m2, and the most abundant fish on inshore coastal reefs of South Australia. Long‐term studies over 18–24 years were conducted at an island reserve site and a fished mainland reference site. At the reserve site the retention rate of fish (reduced by mortality + emigration) was directly correlated with female mean size; the female:male sex ratio ranged from 10 to 20:1, consistent with an induction‐inhibition model of sex‐change. At the fished reference site, female mean size declined under intense fishing, and the sex ratio became strongly skewed towards females. Additional spatial surveys over >2000 km of coast showed that: (1) juvenile and adult abundance was variously determined by habitat features, such as substratum‐type, depth, bottom relief, wave exposure and algal canopy cover, and by geographical factors, such as distance off‐shore and within gulfs; and (2) that female mean size and the sex ratio were strongly influenced by recreational fishing, and to a small extent by bottom relief and other factors. The results suggest that female mean size and the sex ratio together can be used as an indicator of recreational fishing intensity at local scales. As populations of sequential hermaphroditic species are sensitive to size‐selective harvesting, management measures should aim to prevent sperm limitation, reproductive failure and skewed sex ratios in this species.

Clutch and egg size of the tropical lizard Tropidurus torquatus (Tropiduridae) along its geographic range in coastal eastern Brazil

The tropidurid lizard Tropidurus torquatus (Wied, 1820) has a set of populations inhabiting coastal sand dune habitats (“restinga”) along the eastern Brazilian coast. Despite its wide geographic range, there is no information about geographic variation in reproductive features among its populations. In the present study we compared some reproductive aspects of females in 10 coastal populations of T. torquatus, aiming to evaluate to what extension they vary geographically. The minimum size at maturity was relatively similar to most populations, but mean female body size had a considerable variation. Clutch size of almost all coastal populations of T. torquatus had little variation and was composed predominantly of two eggs. Interpopulational variation in the mean egg volume was relatively wide and strongly influenced by the variation in mean female body size. The data of the present study indicated that females of almost all coastal populations of T. torquatus produce, predominantly, clutches with two eggs and invest more energy in egg size instead of clutch size, probably as a consequence of morphological and environmental factors. The increased reproductive investment in egg size was confirmed by the values obtained for the relative clutch mass, which remained relatively constant along the coastal geographic distribution of T. torquatus.

Temporal Changes in Size at Maturity and Their Implications for Fisheries Management for Eastern Bering Sea Tanner Crab

Tanner crab (Chionoecetes bairdi) in the eastern Bering Sea are primarily distributed in Bristol Bay and around the Pribilof Islands. Summer trawl survey data in these two areas were used to estimate mean sizes at maturity for female Tanner crab from 1975 to 2006 and sizes at 50% morphometric maturity for male Tanner crab from 1990 to 2006. Estimated mean sizes at maturity for females showed a statistically significant downward trend in both areas. Sizes at 50% morphometric maturity for males have declined significantly since 1990, in Bristol Bay only. In Bristol Bay, the distribution centers of female Tanner crab have shifted southwest over time and the decrease in female mean size at maturity was significantly related to changes in longitude and bottom depths. Because of terminal molt at maturity, the decrease in size at maturity has important implications for fisheries management: under the current size limit, a smaller proportion of males grow to legal size and therefore a higher proportion of large-growing males are removed by the fishery before they have a chance to participate in reproduction. With the recent maturity at a small size, reduction of the current harvest rates and size limit while maintaining current fishing gear requirements will result in higher yield and higher male spawning biomass per recruit than those under the current harvest strategy.

Geographic trend in sexual size dimorphism and body size of Osteopilus septentrionalis (Cuban treefrog): implications for invasion of the southeastern United States

We collected Osteopilus septentrionalis from Central Florida for analysis of sexual size dimorphism and compared our data to published information from populations across the native and introduced range of the species. We found significant sexual size dimorphism (females larger), with the degree of dimorphism decreasing with increasing degrees north latitude, a trend largely driven by a pronounced decrease in female mean snout to vent length. Potential explanations for this trend include reduced growth rates, increased time to maturity, and reduced life expectancy, all of which may be tied to climatic variation. A trend of decreasing female mean size toward the northernmost extent of the current introduced range of this species may be indicative of diminished impacts and invasive success. Geographical variation in morphology and its associated implications should be evaluated when considering the potential impacts of invasive species.

Reproductive patterns in syntopic terrestrial isopod species (Crustacea, Isopoda, Oniscidea) from Morocco

Summary We compared the reproductive patterns of nine syntopic species of terrestrial isopods from the Oued Laou catchment area, Morocco, with respect to (1) species-specific breeding phenology and (2) reproductive allocation in species of different sizes using laboratory survey data collected over 3 years. All but one species were characterised by seasonal reproduction followed by a sexual rest phase, while ovigerous females of Porcellionides sexfasciatus were present throughout the entire study. Egg production started in April for Philoscia sp., Porcellio dalensis , Porcellio laevis and Porcellionides pruinosus , in May for Armadillidium granulatum and Soteriscus gaditanus , and in June for Agabiformius lentus and Porcellio sp. Thus, under normal environmental conditions, the studied syntopic isopod species exhibited a high degree of overlap in breeding phenology, but species-specific mean female size was negatively correlated with the date of breeding onset; smaller species started breeding later in the year than large species. Several other life-history traits also correlated with species-specific female size. Fecundity was positively correlated with female size in all studied species. The duration of the marsupial period, when the brood pouch contains eggs, embryos or mancae, varied between studied species, lasting 21–24 days in small species ( A. lentus and A. granulatum ) and 49–52 days in large ones ( P. laevis and Philoscia sp.). Reproductive allocation, ranging between 5% ( A. lentus ) and 35% ( P. laevis and P. dalensis ), was positively correlated with female weight. Accordingly, parental investment in producing a juvenile varied between 0.6 mg per manca in the small A. granulatum and 1.6 mg per manca in the large P sexfasciatus . Females of two species reproduced only once in their lifetime. Thus, the smallest of the tested species, A. lentus and A. granulatum are considered semelparous with a low overall reproductive potential of 176 and 320 released juveniles, respectively. By contrast, the iteroparous species P. laevis and P. dalensis exhibited the highest reproductive potential of 2640 and 2432 (juveniles released), respectively; producing, in total, more than six times the offspring of semelparous species. We discuss these findings in the context of species-specific reproductive strategies of co-existing syntopic species.

Intraspecific density-dependent effects on growth and fecundity of Diplosentis nudus (Harada, 1938) Pichelin et Cribb, 2001 (Acanthocephala, Cavisomidae)

AbstractDuring June and July of 2007, a total of 130 specimens of the fish Rastrelliger kanagurta Cuvier (Teleostei, Scombridae), ranging between 19–31 cm in total length, were caught in the Red Sea off the coast of Sharm El-Sheikh, South Sinai, Egypt, and examined for infections by acanthocephalans (65 fish/month). Of this number, 29 (22.30%) were slightly or heavily parasitized by the acanthocephalan Diplosentis nudus (Harada, 1938) Pichelin et Cribb, 2001 (Cavisomidae); no other helminth parasites were found in the intestine of R. kanagurta. Twenty-nine infrapopulations of D. nudus, ranging from 23–218 individuals were collected from the infected fishes. These infrapopulations were distributed in a well-defined fundamental niche along the intestine of R. kanagurta, where the distribution of male worms was not random with respect to female worms size and position and suggests that the male-male competition for access to female may be intense and may select for large males. No correlation between fish size and infrapopulation size was observed. Correlations between female-to-male sex ratio and infrapopulation size, numbers of females and their mean lengths, numbers of males and their mean lengths, mean female length and mean male length within infrapopulation were very strong, and clearly suggest that as the infrapopulation size increased, the number of females and their mean lengths decreased and the number of males and their mean lengths increased. Combination of these results strongly suggests density-dependent effects and competition between male worms. The relationship between the mean female length or size and the number of eggs within its pseudocoel was strongly positive; egg production by female worm significantly decreases as the infrapopulation size increases, suggesting density-dependent reduction in female worm fecundity. Tendency for the variability in male testes size was not significant in infrapopulations of D. nudus. All of these results are discussed.

Size and fecundity variation in populations of Poecilia vivipara Block & Schneider (Teleostei; Poeciliidae) inhabiting an environmental gradient

The reproductive variables [female size (geometric centroid size), fecundity and offspring size (longest diameter of the embryo)] of the livebearer Poecilia vivipara in the quaternary lagoons of northern Rio de Janeiro State varied significantly among sites and were partially associated within and among sites. Mean female size was directly related to salinity. Fecundity (number of offspring) was directly related to female size both within and among sites. The female size × fecundity relationship, however, was not constant among sites. Offspring size was partially and directly associated with female size and salinity. The relationship between fecundity and female size was positively related with fecundity, suggesting a non‐linear relationship of these variables when the total sample was considered. The results suggest that life‐history differences among sites were more related to different predation regimes than to simple effects of plasticity caused by increased growth in saltwater environments.

New Distribution Records of Sergestid Shrimp, Acetes intermedius (Decapoda: Sergestidae) from Peninsular Malaysia with Notes on its Population Characteristics

Present research records for the first time, the occurrence of the sergestid shrimp Acetes intermedius in Peninsular Malaysia. A taxonomic account of this shrimp is provided. Notes on its habitat and population characteristics were examined based on 995 specimens collected from the Klebang Besar, coastal waters of Malacca, Peninsular Malaysia during February 2005 to January 2006. Size-frequency distribution revealed that the mean size of females consistently exceeded that of males throughout the year (TL range: 15-27.50 and 13.50-33 mm for males and females, respectively). The overall yearly and the monthly sex ratio were in favor of females. Asymptotic length (L4) and growth co-efficient (K) was estimated as 34.65 mm and 1.50 yearG1. The exponent b (2.979) of the length-weight relationship for males was found near to the isometric value (b = 3.0) and positive allometric growth was observed in females and combined sexes (b = 3.227 for females and b = 3.249 combined sexes). The asymptotic weight was calculated as 211.21 mg. The overall average growth rate of A. intermedius showed 2.10 (` 0.88) mm/month in the coastal waters of Malacca.

Female preference variation has implications for the maintenance of an alternative mating strategy in a swordtail fish

Female preference variation over space and time could be an alternative to frequency-dependent selection as a mechanism maintaining alternative male reproductive strategies. In the swordtail fish, Xiphophorus nigrensis, males have alternative strategies where large courting males (courters) and smaller males (sneakers) have equal fitnesses due to a mating advantage for the courters and a higher probability of reaching sexual maturity for the sneakers. Variation in one of these advantages over space or time may be the mechanism that maintains these two strategies. We examined female preference variation for the courting strategy in Xiphophorus multilineatus, a species with the same strategies. Females had an overall significant preference for courters. The strength of this preference was positively related to female size, with smaller females having a weak preference for courters. If the relationship between female size and strength of preference is consistent over space and time, more smaller females would result in an weaker preference for courters, which would increase the relative mating advantage of sneakers. We assessed female size distribution and the frequency of each strategy across space and time and detected significant differences in mean female size across subpopulations and across time, as well as a relationship between mean female size and the relative frequencies of the two male strategies: courters were significantly more common in those samples with the largest females. These results suggest that variation across subpopulations of X. multilineatus in female preferences over space and/or time could shift the balance in fitness between the two strategies.

MORPHOMETRIC VARIATION AND ITS EFFECT ON REPRODUCTIVE POTENTIAL IN FEMALE COLOMBIAN SLIDER TURTLES (TRACHEMYS CALLIROSTRIS CALLIROSTRIS)

We evaluated morphometric variation and reproductive effort in Trachemys callirostris callirostris females from nine populations in the Mompos Depression of northern Colombia. Two hypotheses were evaluated: (1) phenotypes of nesting females co-vary according to geographic distances among sites and/ or specific environmental conditions at each site, and (2) female body size influences their reproductive potential and offspring characteristics. Populations were shown to differ in both mean female body size and body shape, with differences more related to local habitat characteristics than to geographic distances among sites. Larger females occurred in sites with higher annual precipitation and lower hunting pressure. Female size was highly correlated with clutch size and mass. Although habitat characteristics affected female size, habitat alone was not a predictor of reproductive potential. Specific habitat conditions and hunting both influence female phenotypes in this region and thereby also influence key demographic parameters, which have clear conservation implications for this highly exploited species.

Variation in egg-size in the Wedge-tailed Shearwater (Puffinus pacficus)

We assessed variation in the size of eggs of Wedge-tailed Shearwaters (Puffinus pacificus) within and between two colonies in eastern Australia. Eggs at Heron Island were significantly larger than at Lord Howe Island. We also found significant between-season variation in size of eggs at Heron Island, with larger eggs being laid in 2005 than 2006. Mean female size (as indicated by tarsal length) did not differ between the two colonies, or between seasons at Heron Island. However, as with other seabird species, larger females produced larger eggs. Overall, our results imply that facultative changes in female reproductive effort associated with changes in availability of resources are not the main cause of variation in egg-size in this species. The consistently smaller size of eggs for birds at Lord Howe Island compared with those from Heron Island suggests that obligate processes (e.g. natural selection) are more likely to be responsible.

Adaptive preferential selection of female coccinellid hosts by the parasitoid wasp Dinocampus coccinellae (Hymenoptera: Braconidae)

Females of the parasitoid wasp Dinocampus coccinellae are known to parasitise both male and female coccinellid hosts. It is suggested that female hosts provide more resources for developing wasp larvae because they tend to be larger than male hosts, and female coccinellids have a much greater food intake than males. Thus the wasp's lifetime reproductive success should be increased by ovipositing preferentially in female rather than male hosts when given a choice. Laboratory experiments, using Coccinella septempunctata as a host, show that such a preference does exist. Wasps preferentially oviposit in females, and this preference is not simply a result of the larger mean size of females compared to males. These results corroborate higher rates of prevalence in female compared to male hosts reported previously.

Daily cycle and body characteristics of mating Litopenaeus vannamei shrimps (Decapoda: Penaeidae) in the wild off southern Sinaloa, Mexico

Mating behavior has been described for very few species of penaeoid shrimps. We describe some of the environmental conditions under which mating of Litopenaeus vannamei took place in the ocean, as inferred by the presence of attached spermatophores on the thelycum of females, combined with the presence of mature males with empty ampulla terminalis, both evidence of recent copulation. Out of a total of twelve 24 hr samplings on board the research vessel B/O "EL PUMA", one was selected to examine mating. There were four periods of observation. The highest frequency of females with attached spermatophores were found during the daytime whilst the lowest was registered during the night. Females with attached spermatophore were mostly at stages IV and V of ovarian maturity and fell within the 30-50 mm of C.L. range. Copulating male size ranged between 30 and 40 mm of C.L. and there was a close relation between the percentage of mating females and males. Male to female ratio varied throughout the sampling period but it was never 1:1. The female mean size was, in all cases, bigger than the male mean size. Among the environmental factors, salinity and oxygen varied very slightly throughout the sampling period; temperature variation was more pronounced and those changes were attributed to the tidal oscillation.

Population Structure and Reproduction of the Deep-Water Shrimp Plesionika Martia (Decapoda: Pandalidae) from the Eastern Ionian Sea

The population dynamics, growth, and reproduction of the deep-water pandalid shrimp Plesionika martia were studied in the eastern Mediterranean Sea. Samples were collected monthly (July 1999–June 2000) at a depth range of |$440 - 600\;{\rm{m}}$| between Zakynthos Island and Peloponnissos (eastern Ionian Sea, Greece). Additional samples were taken in April and May 2001. Size-frequency distribution revealed that mean female size consistently exceeded that of males throughout the year (CL range: |$8 - 23.5\;{\rm{mm}}$| and |$9.3 - 29.1\;{\rm{mm}}$| for males and females, respectively). Smaller individuals of both sexes occurred only at depths less than 500 m. Mean size of both sexes increased linearly with depth, whereas a less prominent trend of sex ratio in favor of females by depth was observed. The overall yearly and the monthly sex ratio were in favor of females except during winter, when the two sexes were equally represented. Carapace length–wet weight relationships showed negative allometry, for both males and females. Ovigerous females occurred year around, although the main reproductive season extended from April to October. The smallest ovigerous female was |$11.8\;{\rm{mm}}\;{\rm{CL}}$|⁠, whereas the size at |$50\% $| sexual maturity |$({\rm{C}}{{\rm{L}}_{{\rm{m}}50}})$| was estimated as |$16.16\;{\rm{mm}}$|⁠. Fecundity and reproductive output were found loosely related to shrimp size. The von Bertalanffy growth curve parameters were estimated as: |${L_\infty } = 30.6\;{\rm{mm}}, k = 0.31\;{{\rm{year}}^{ - 1}}$| in females and |${L_\infty } = 28.2\;{\rm{mm}}, k = 0.53\;{{\rm{year}}^{ - 1}}$| in males. Regarding the major life history traits, P. martia from the eastern Ionian seemed to conform to those in other Mediterranean areas. Nevertheless, some population differences exist, which can be related to the oligotrophic conditions and the lack of fishing pressure in the studied area.

Individual variation in the rate of use of tree-hole tools among wild orang-utans: implications for hominin evolution

Primate tool use varies among species, populations, and individuals. Individual variation is especially poorly understood. Orang-utans in the Sumatran swamp forest of Suaq Balimbing varied widely in rates of tool use to extract honey, ants or termites from tree holes and in the degree to which they specialized on this tree-hole tool use. We tested whether individual variation was best explained by effects of social dominance, habitat differences, or by opportunities for socially learning the skills during ontogeny. There was no evidence for the first two hypotheses. However, we found a strong relationship between tool use specialization and mean female party size, which was used as a proxy for the opportunities for socially mediated learning in a foraging context during their development. This use was justified because females are rather philopatric and their mean party size remained stable over time, thus reflecting long-term tendencies. The correlation was not an artifact of a direct effect of party size on tool use tendencies, and did not hold for males, the dispersing sex. Thus, variation in the number of opportunities for social learning explains tool use variation within populations, corroborating hypotheses for between-population variation. The emergence of human culture was accompanied by vastly improved mechanisms of social learning. In order for these improvements to be favored by natural selection, the cultural potential must have actually been expressed. Thus, a combination of strong sociability and a reliance on tool-using or other technical skills acquired through social learning must have characterized early hominins.

Last Eggs in White-winged Tern Clutches Are Not Smallest; Are Marsh Terns Different from Other Larids?

Terns of the genus Chlidonias may be exceptional among the larids in laying the ultimate egg in the clutch-sequence that is not smaller than the earlier eggs. To investigate this, we analyzed data on egg length, breadth, volume and shape in three-egg clutches of the White-winged Tern (Chlidonias leucopterus) breeding in NE Poland. Both length and volume of the c-egg was larger than mean values the a- and b-eggs in the clutch. They also differed in shape. Egg breadth did not differ in such a comparison. Two species of Chlidonias terns do not conform to the typical pattern of larids, in which the last-laid egg is the smallest in the clutch; this may be related to their being insectivorous rather than piscivorous. Chlidonias terns lay eggs of the size expected from the regression of mean egg size on mean female body size in all the Western Palearctic terns.

Distribution and population structure of the red shrimp ( Aristeus antennatus) on an unexploited fishing ground in the Greek Ionian Sea

The distribution and population structure of the red shrimp, Aristeus antennatus, were investigated for an unexploited fishing ground in the Greek Ionian Sea (middle-eastern Mediterranean). A total of 8 618 specimens, 7 273 females and 1 345 males was caught during a 12-month survey, from January to December 1997, at depths ranging from 400 to 800 m. Monthly size frequency distributions were analysed using different techniques, resulting in estimates of growth and mortality. Carapace lengths (cephalothoracic lengths, CL) ranged between 12 and 62 mm for females and 9 and 45 mm for males. The mean size of specimens exhibited statistically significant differences in relation to sex and months. Recruitment of both sexes occurred in mid-winter (January). Only the mean size of females seemed to increase with depth. Estimation of the von Bertalanffy growth parameters revealed high k values and a life expectancy of 4 and 5 years for males and females, respectively. A high percentage of specimens bore spermatophores during May and August, indicating that these months were peak breeding periods. Natural mortality rates ranged from 0.55 to 0.70 for females and from 0.62 to 0.79 for males, depending on the method used. Based on its biology and population dynamics, it appears that the red shrimp population in the study area has the potential to support a viable fishery.

Demographic Parameters of Golden Spotted Rock BassParalabrax auroguttatusfrom the Northern Gulf of California

The sex ratios, growth, and mortality of the golden spotted rock bass Paralabrax auroguttatus (Serranidae) were determined for populations from Islas Encantadas and Bahía de los Angeles in the Gulf of California. Specimens ranged from 137 to 479 mm standard length and from 135 to 3,100 g. Sagittal otoliths were used to determine age. A von Bertalanffy model of growth for both populations combined was estimated as Lt = 474.4·(1 − e−0.115(t+ 2.093)), where Lt is fish length at age t. This model is comparable to those for other rock basses. The relationship between length and weight (W) followed the power function W = 0.00002·L3.0797 (r2 = 0.96) with no difference between males and females. The mortality rate was estimated as 49% per year for fish of age 5 and older. In our Bahía de los Angeles samples, the sex ratio was significantly skewed, with more males than females. The mean size of females was significantly smaller at Bahía de los Angeles than in Islas Encantadas. Examination of the sex ratios for these two populations suggested that this species is gonochoristic.