Male emergence timing and mating success in the funnel-web spider,Agelena limbata (Araneae: Agelenidae)

Field observations on the relationship between male mating success and emergence timing in the funnel-web spider,Agelena limbata, were conducted.Agelena limbata is an annual species and adult males appear slightly earlier than adult females in July. As males deposit a copulatory plug at the female epigynum after copulation, copulation with virgin females is important to males. The number of copulations in males with virgin females, which strongly correlates with the longevity of males and the number of females that males courted, did not correlate with the emergence timing of males. Early emerged males and females were significantly larger in size than later ones, but the correlation coefficient between the emerged date and the cephalothorax width was not strong. Males that emerged earlier did not have any advantage in copulating with larger and more fecund females. Furthermore, virgin females first copulated on average 7.9 days after their final molt and the mortality rate of adult males increased after the final molt. These factors may favor the smaller degree of protandry in male emergence timing inA. limbata.     

Effects of size at metamorphosis on stonefly fecundity, longevity, and reproductive success

Many organisms with complex life cycles show considerable variation in size and timing at metamorphosis. Adult males of Megarcyssignata (Plecoptera: Perlodidae) are significantly smaller than females and emerge before females (protandry) from two western Colorado streams. During summer 1992 stoneflies from a trout stream emerged earlier in the season and at larger sizes than those from a colder fishless stream, and size at metamorphosis did not change over the emergence period in either stream. We performed two experiments to determine whether variation in size at metamorphosis affected the fecundity, reproductive success and longevity of individuals of this stonefly species and if total lifetime fecundity was affected by the number of matings. In the first experiment, total lifetime fecundity (eggs oviposited) was determined for adult females held in small plastic cages in the field. Males were removed after one copulation, or pairs were left together for life and allowed to multiply mate. Most copulations occurred in the first few days of the experiment. Females in treatments allowing multiple matings had significantly lower total lifetime fecundity and shorter adult longevity than females that only mated once. Multiple matings also reduced longevity of males. Fecundity increased significantly with female body mass at emergence, but only for females that mated once. While multiple matings eliminated the fecundity advantage of large female body size, number of matings did not affect the significant positive relationship between body mass at metamorphosis and longevity of males or females. In a second experiment designed to determine if body mass at emergence affected male mating success, we placed one large and one small male Megarcys in an observation arena containing one female and recorded which male obtained the first mating. The large and the small male had equal probabilities of copulating with the female. Copulations usually lasted all night, and the unmated male made frequent, but unsuccessful attempts to take over the copulating female. Our data suggest that selection pressures determining body size at metamorphosis may operate independently on males and females, resulting in evolution of sexual size dimorphism, protandry, and mating early in the adult stage. We emphasize the importance of interpreting the fitness consequences of larval growth and development on the timing of and size at metamorphosis in the context of the complete life cycle. Received: 1 July 1997 / Accepted: 12 November 1997     

Hibernating patterns of free-ranging Columbian ground squirrels

Summary The patterns of torpor and euthermy during hibernation was documented for 28 free-ranging Columbian ground squirrels (Spermophilus columbianus) fitted with temperature-sensitive radio transmitter collars. Adult males began hibernation earlier, were euthermic for a greater proportion of the hibernating season and emerged earlier than other age and sex classes. The patterns of hibernation of adult females did not differ significantly from those of juveniles. Emergence from the hibernaculum was preceded by a long (3–12 d) euthermic interval in adult males but not in adult females or juveniles. Changes in soil temperature did not appear to initiate emergence. The greater time spent euthermic by adult males is interpreted as a significantly greater energy cost of hibernation for adult males than for other age and sex classes. The benefits offsetting these costs may be increased reproductive potential in spring and avoidance of predation in late summer.     

Sexual differences in growth strategies of the wolf spider Hygrolycosa rubrofasciata

In invertebrates, the size at maturation is considered to be important for adult fitness. In the wolf spider Hygrolycosa rubrofasciata, however, it is only females that clearly benefit of larger size through augmented egg production, while male mating success is determined by display activity not related to size. Thus, we can expect conflicting growth patterns for the sexes. Additionally, populations differ greatly in adult size: individuals from dry habitats are smaller than those from wet habitats. To study the sexual differences in reaction norms of growth, we reared spiderlings from seven populations at two food levels under controlled laboratory conditions and compared size at sexual maturity. The shapes of reaction norms for adult size differed between the sexes. In females, the reaction norms were parallel, but individuals from dry habitats tended to grow larger at the given food levels. In males, there was a significant interaction between food level and population without any consistent differences between populations. Maturation time was a plastic character in both sexes with no genetic differences among populations. However, females on low food level matured later and significantly smaller in size than those on high food level. Males also matured later on low food level, but they were nearly of the same size as males that received more food. Female growth patterns reflected the strong selection for large size at maturity. However, the patterns for males were highly variable, which could be explained by the weak overall selection on male size, which means that any environmental factors can affect male growing patterns. This revised version was published online in November 2006 with corrections to the Cover Date.     

Effects of host stage on the development of the facultative autoparasitoid Encarsia tricolor (Hymenoptera: Aphelinidae)

Encarsia tricolor is a facultative autoparasitoid of the glasshouse whitefly, Trialeurodes vaporariorum, with a potential in biological control. The rate of development, number of mature oocytes at emergence, number of ovarioles and size of the emerged adults were studied. Five nymphal instars (N1, N2, N3, N4, and pharate adult) of T. vaporariorum were used as hosts for the females. Female larvae and pupae of E. tricolor and Encarsia formosa were used as hosts for the males. Females developed faster when the egg was laid on N3 (18.0 days from egg to adult) and slower on N1 (22.3 days). Females were bigger when developing from N1 and N3 than from N4 and pharate adult. On emergence the mean number of mature oocytes was always small (0.8–2.6). Males developed faster and were smaller than females, and developed faster and were larger on larvae of E. formosa.     

Sex Biased State Dependence in Natal Dispersal in Desert Isoponds, Hemilepistus reaumuri

Differences in the emergence, movement, and settling patterns of individuals during natal dispersal can provide testable hypotheses about the costs and functions of movement. Emergence, movement, and settling patterns were studied in desert isopods, Hemilepistus reaumuri. The young of this semelparous, monogamous, crustacean emerge from their natal burrows each spring and search for sites to establish new burrows or gain acceptance as mates in occupied burrows. Dispersal was measured in a long, narrow corridor into which individuals marked after emergence were monitored. Females emerged slightly earlier than males with substantial overlap. Size or condition varied with time before settling differently in males and females. Isopods in good or poor condition did not differ in distance traveled, but males in good condition took more time before settling. Small males were more likely to start new burrows and took less time before settling, suggesting they might be acting in anticipation of losing contests for female-initiated burrows. Larger females and those in higher condition were more likely to start new burrows and took less time before settling. The pattern in females could reflect male choice or constraints or costs associated with burrow establishment in females, which should be tested. Measures of dispersal based on recaptures of traveling or recently settled individuals may differ from the distribution of successful reproduction. In this study travelers were observed at shorter average distances than settlers, but successful settlers traveled less far than unsuccessful ones.     

Protandry and postandry in two related butterflies: conflicting evidence about sex-specific trade-offs between adult size and emergence time

Natural selection acting on timing of metamorphosis can be sex-specific, resulting in differences in timing between males and females. Insects with discrete generations frequently show protandry: males usually mature before females. Both Euphydryas editha and E. aurinia butterflies followed this trend. The present study was motivated by the unusual observation of consistent postandry in addition to protandry. In a single E. editha population observed over 20 years the emergence period of males was longer than that of females, both the first and last emerging individuals being males. Variance of timing among individual E. editha larvae is imposed by spatial patchiness of the snowmelt that releases them from winter diapause. If individual larvae released late from diapause were to compensate for their lateness by shortening their development times, they would be small at maturity. If such compensation were only partial, they would be both late and small. Size and timing would become associated. If females were more prone to such partial compensation than males, the observations of postandry could be explained and the prediction made that any tendency for late individuals to be small should be stronger in females than in males. This was the case: in 1 year late males were the same size as early males, in a second year they were larger. Late females were significantly smaller than early females in both years. In E. aurinia, results were opposite both to theoretical prediction and to the observations from E. editha: although the male emergence period was longer than that of females exactly as in E. editha, late males were smaller than early ones, while late females were not small. The data from E. editha support the hypothesis of a sex-specific trade-off between size and emergence time, the data from E. aurinia do not.     

Effects of sugar feeding on carbohydrate and lipid metabolism in a parasitoid wasp

Lifetime patterns of carbohydrate and lipid metabolism were compared in starved and sucrose‐fed adults of the parasitoid Macrocentrus grandii (Goidanich) (Hymenoptera: Braconidae). As expected, sucrose‐fed individuals lived longer than did starved individuals. Macrocentrus grandii males and females eclosed with levels of simple storage sugars (presumably primarily trehalose) and glycogen that were below maximum levels recorded from sucrose‐fed parasitoids. Both of these nutrients dropped to very low levels in starved individuals within 4 days post‐emergence and were maintained at high levels in sucrose‐fed individuals throughout their lives. Lipid reserves at emergence represented the highest lipid levels for both sexes in the two diet treatments, with levels declining over the lifetimes of males and females from both diet treatments. Our results therefore suggest that dietary sucrose is used to synthesize trehalose and glycogen, but not lipids in M. grandii. Also, in contrast to the patterns observed for the simple sugars and glycogen, lipid levels in starved individuals did not drop below levels observed in sugar‐fed individuals. The average number of mature eggs carried by females at emergence was 33 and increased to approximately 85 in sucrose‐fed and 130 in starved females by the age of 5 d in the absence of hosts. The egg maturation rate was therefore higher in starved than in sugar‐fed females. Potential explanations for this unexpected result are discussed.     

Emergence rhythms and protandry in relation to daily patterns of locomotor activity inTrichogramma species

Summary In insect parasitoids, the mating structure of the population depends on the emergence pattern of adults and on their behaviour after emergence. In order to study some aspects of these characteristics in four species of egg parasitoid of the genusTrichogramma, laboratory experiments using automatic video analysis are performed. Adult emergence is concentrated in the morning, with an earlier time for males. The variability of the time of emergence is under genetic control. The relationships between the emergence pattern and the locomotor activity are considered by measuring individually: first, the delay between the emergence and the first locomotion which is significantly greater in females than in males and, second, the activity of newly emerged males, which is maximum at the time of the emergence of females. The locomotor activity is influenced by mating; mated females are much more active than virgin ones, mated males are less active than virgin ones. The adaptive values of the rhythmicity of emergence and of protandry are discussed together with their relationship with the patterns of locomotor activity. The results are also considered with respect to mating strategies in insect parasitoids; they actually support the hypothesis of mating occurring principally among individuals native to the same host patch inTrichogramma species.     

Occurrence of protandry and a female-biased sex-ratio in a sponge-associated water mite (Acari: Unionicolidae)

The sex ratio of aUnionicola crassipes-type mite from a pond in Alberta, Canada, was found to be significantly female-biased at the time of adult emergence. Male mites emerged earlier, but were later surpassed in number by the females. This protandry seems more likely to be due to the smaller size of the males and hence their faster developmental rate than to any mating advatage the male mites gain by early emergence. It is possible that group selection acting on the productivity of mite colonies with different proportions of low-sex-ratio producers has selected for female-bias. Water mites are not known to exhibit any atypical modes of reproduction (e.g.arrhenotoky), nor is it known whether pre-adult maleU. crassipes have a greater mortality rate than females, so the mechanism behind the skewed ratio is not known.     

Sequences and timing of dental eruption in semi-free-ranging mandrills (Mandrillus sphinx)

The chronology of tooth emergence is often used to examine the growth and development of individuals and to compare life histories across species. Emergence patterns are also used to age animals and to infer life history influences for extinct species. However, comparative studies of primates are hindered by a lack of dental development data for many species. Here we describe the sequences and timing of tooth emergence for a large sample of semi-free-ranging mandrills (Mandrillus sphinx) and compare this with other life history variables for this species. Deciduous dentition emerged in the sequence i1 i2 c p3 p4. The augmented sequence (including information about variability in emergence sequence) was i1 i2 [c p3] p4 for the female maxilla and the male mandible, and i1 i2 c p3 p4 for the female mandible and the male maxilla. Deciduous dentition was complete by 5.0 months in females and 6.4 months in males. The permanent dentition began to emerge at 26 months, and complete adult dentition had emerged by 68 months for males and 85 months for females. Sex differences occurred in the augmented eruption sequences: females M1 I1 I2 [M2 C] P3 P4 M3, males M1 I1 [I2 M2] [P4 = P3 = C] M3. The order of tooth eruption and the occurrence of sequence polymorphisms were very similar to those observed for baboons and macaques. Comparison with life history variables showed that mandrills have complete deciduous dentition at weaning, females possess both adult incisors and M1 when they first reproduce, but still have deciduous canines and premolars, and that both sexes have full adult dentition before they attain their full adult stature and mass.     

引进花角蚜小蜂成虫的寿命和羽化节律

通过室内饲养和连续观察,研究了食物、温度对引进花角蚜小蜂成虫寿命的影响及其羽化的时间节律.结果表明：食物对该寄生蜂成虫寿命有极显著影响,喂食20％蜂蜜或20％蜂蜜＋新鲜松针可将雌虫寿命从不喂食的1.5 d延长到14.8 d和17.3 d,将雄虫寿命从不喂食的1.5 d延长到11.3 d和12.3 d.喂食20％蜂蜜条件下,温度也表现出极显著影响,23 ℃和26 ℃下雌、雄成虫的寿命均明显较长,32 ℃下均最短,相同温度下雌虫的寿命显著长于雄虫.日周期中,雌虫主要在11:00-15:00羽化,18:00以后基本不羽化;雄虫主要在9:00-12:00羽化,17:00以后基本不羽化.在花角蚜小蜂的主要羽化期7-9月,7月羽化量最大 ,此后8、9月呈波浪式递减;单日羽化的成虫中,雌虫大多占80％以上,雄虫则长期在一个较低水平波动.对比试验发现,花角蚜小蜂在收蜂棚中的出蜂量比在收蜂箱中更大.花角蚜小蜂在羽化前积累的能量十分有限,人工放蜂前提供必要的营养补充将有助于提高生物防治效果.福建和广东夏季的高温、花角蚜小蜂雌成虫和松突圆蚧雌成蚧虫口高峰期不吻合、极高的雌性比例等是影响该寄生蜂种群稳定的潜在因素.收蜂棚有利于大量收集花角蚜小蜂,适合在生产上应用.     

Intranidal mating,emergence, and sex ratio in a communal beeAndrena jacobi Perkins 1921 (Hymenoptera: Andrenidae)

The extent of preemergence intranidal mating, schedules of emergence, and sex ratio at emergence were documented forAndrena jacobi, a communal, univoltine bee, by collecting and dissecting adults as they emerged from their fossorial nests in 1994. Over 70% of females had mated intranidally with nestmate males, thus potentially incestuously, before emerging. Preemergence intranidal mating did not vary during a day or between nests within a day, though it was less frequent at the start and end of the period of emergence. It was independent of a female's size.A. jacobi was protandrous, though some males emerged after all females. The sex ratio at emergence was remarkably female biased, possibly a consequence of local mate competition. Intranidal mating may represent a characteristic trait of communal bees where a high density of receptive females are predictably aggregated within a nest.     

Age structure and body size of the Chuanxi Tree Frog Hyla annectans chuanxiensis from two different elevations in Sichuan (China)

Age, body size, and growth patterns in the subtropical anuran Hyla annectans chuanxiensis from high (Dengchigou Protection Station) and low (Lingguan Town) elevations in Baoxing County of Sichuan province (China) were described using skeletochronology. Females were significantly older than males at the low-elevation site, but there was no significant difference between the sexes at the high-elevation site. Age at sexual maturity of both males and females was 2 years at the high-elevation site, whereas males matured at 1 year and females at 2 years at the low-elevation site. Males and females from the low-elevation population reached a maximum age of 3 and 4 years, respectively, whereas males and females from the high-elevation population reached a maximum age of 4 and 5 years, respectively. At both sites, females were significantly larger than males. Females and males from the high-elevation population were larger than individuals from the low-elevation population. When the effect of age was controlled, the differences in body size of the two populations were significant only for females. Von Bertalanffy growth curves indicated that the growth rates in males was greater than in females in both populations. They also showed that the growth of both sexes slowed at an earlier age in the low-elevation population than in the high-elevation population. The findings suggest that age is a major factor underlying body size patterns for both sexes, but that the elevation of the locality affects the body size of females.     

Sexual size dimorphism and sex-specific survival in adults of the damselfly Lestes disjunctus

1. A population of adult Lestes disjunctus (Odonata: Lestidae) was studied in eastern Ontario, Canada. Mass at sexual maturity and activity rates of individuals were measured. Population density was estimated on transects, while survival rates and population size were estimated using mark−recapture methods.
2. There was no difference in mass of mated and unmated males. Females were more than 50% heavier than males, and were also more active than males.
3. Males were almost eight times more abundant on transects than females, but Manly−Parr estimates of male population size were only a maximum of 2.5 times larger than estimates for females.
4. Males were 2.5 times more likely to be resighted after marking than were females. This accounts for much of the discrepancy between transect estimates and mark−recapture estimates of relative population size.
5. Daily survival rates of sexually mature females were not significantly less than those of males, and therefore cannot account for a change in sex-ratio from 1 : 1 at emergence to more males than females in sexually mature adults.
6. Differences in mortality must occur prior to sexual maturity, coincident with the time during which differences in mass gain are also taking place.     

Year-round local movements of the japanese fluvial sculpin,Cottus pollux (large egg type), with special reference to the distribution of spawning nests

Year-round local movements of adult Japanese fluvial sculpin.Cottus pollux (large egg type), were investigated by a capture-mark-and-recapture method from July 1989 to July 1990 in the upper reaches of the Inabe River, central Japan. In the pre-breeding (July to January) and post-breeding seasons (June to July), the mean distance of movements in males and females was less than 20 m, and there was no apparent tendency to move into a particular channel-unit habitat, suggesting residential tendency in both sexes. In the breeding season (February to May), males tended to move into the raceways where most of the spawning nests were found, but females did not do likewise, indicating a sexual difference in movements in that season. Such sexual difference in movements was also confirmed by the records of individuals captured and recaptured more than three times: six (42.9%) of 14 males moved into the raceways in the breeding season, whereas only one (7.1%) of 14 females did so in that season. The reason behind this sexual difference in movements observed in the breeding season is discussed from the viewpoint of the patterns of spatial distribution between sexes during the pre-breeding and breeding seasons.     

Consequences of adult size for survival and reproductive performance in a herbivorous ladybird beetle

Abstract.

• 1 A univoltine herbivorous ladybird beetle Epilachna niponica (Coleoptera: Coccinellidae) shows a large variation in adult size within a population.
• 2 Large adults had higher survival from emergence to the reproductive season, and the size-dependent adult survival was most apparent during hibernation. On the other hand, adult survival during pre-hibernation contributed little to size-dependent overall survival.
• 3 Neither reproductive lifespan nor lifetime fecundity were a function of adult size, though large females produced larger size of egg batches.
• 4 Size of adult beetles was significantly reduced by leaf damage to plants on which they grew up on larval stage. Since leaf herbivory increases through the season, late emerged adults that were subjected to food deterioration during the larval period were smaller than early-emerged individuals.

     

Effects of larval movement behavior and density on emergence success and adult body size in a commensal midge

Changes in larval density and movement behavior of a commensal midge, Nanocladius (Plecopteracoluthus) sp. #4, were monitored for 26 weeks in recirculating laboratory streams. Adults were captured at emergence, sexed, and weighed to assess the effect of larval density and movement behavior on emergence success and adult size. The density of midges on hosts declined with time and coincided with a springtime increase in larval movement frequency. Midges residing on hosts with high spring densities emerged significantly less than midges on hosts with low densities. Resident midge density on hosts did not influence the likelihood of successful colonization by commensals and colonizers showed no preference for initial attachment site on hosts. However, colonizing midges emerged significantly less than resident midges. Similarly, successful emergers changed tube positions significantly less often as larvae relative to non-emergers. There was no difference in adult body weight of resident midges and colonists/movers, but adult males which emerged from commensal-laden (high density) hosts were significantly smaller than males from low density hosts. These data indicate larval density and movement behavior may have strong fitness consequences for commensal midges.     

Sexual size dimorphism, growth and maturity of the Japanese fluvial sculpin,Cottus pollux (large egg type), in the Inabe River, Mie prefecture, central Japan

The population structure of the Japanese fluvial sculpin,Cottus pollux (large egg type), in the upper reaches of the Inabe River, Mie Prefecture, central Japan, was investigated by a mark-and-recapture method from July 1989 to January 1991. Breeding of the species occurred from mid February to early May, peaking from mid February to late March. The mean size of mature males observed in March 1990 was significantly larger than that of females, showing apparent sexual size dimorphism. Data analysis of the growth of 1658 marked individuals revealed that the species matured at 2 years of age in both sexes. Whereas 1 year old males reached ca. 50–70 mm SL, females were less than 50 mm SL at the same age, size dimorphism already being apparent. Immature males exhibited higher growth rates than females during their first and second years, some of the former outstripping mature males of the preceding year class in total length. After attaining sexual maturity, both males and females grew mainly from July to December, with no significant differences in mean growth rate between them. Sexual size dimorphism of the species seems to be attributable to different growth rates between the sexes during their immature stage.     

Population structure and emergence order in the fruit-bat (Rousettus aegyptiacus: Mammalia, Chiroptera)

Population size and emergence order of R. aegyptiacus were studied in the Abas cave. Haifa, Israel. Throughout the reproductive period adult females populated the cave and the adult population consisted mainly of adult females except during winter when higher numbers of adult males were recorded. The proportion of juveniles increased consistently from spring to winter. Thus, it is suggested that the Abas cave serves as a maternity roost. Adult females in the reproductive state emerged from the cave earlier that juveniles and adult males. Social factors and differences in nutritional demands which may correspond to this different emergence order are discussed.