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.     

FITNESS CONSEQUENCES OF MATING SYSTEM,SEED WEIGHT,AND EMERGENCE DATE IN A WINTER ANNUAL,COLLINSIA VERNA

Selfed and outcrossed progeny of 60 maternal parents were produced to investigate the joint and individual effects of mating system, seed weight, and emergence date on the expression of characters related to fitness and adult fecundity. A series of analyses of variance investigated these effects through time and indicated that 1) mating system explained 56% of the variance in seed weight, 2) seed weight explained 51% and mating system explained 38% of the variance in emergence date, and 3) mating system explained 71% and seed weight explained 15% of the variance in fecundity. Outcrossed-seed means differed significantly from selfed-seed means for all traits measured. On average, outcrossed seeds were larger, germinated earlier, had higher percentage emergence, and produced plants that were more fecund than selfed seeds. The coefficient of inbreeding depression increased through time in this study, from 0.05 for seed weight to 0.23 for fecundity. Seed weight and emergence date were positively correlated, both phenotypically and genetically, for both mating systems. Genetically, this indicates that genes that increase the value of seed weight also increase the value of emergence date and vice versa. Phenotypically, the positive correlation indicates that larger seeds germinate later. Outcrossed seeds were significantly larger but germinated earlier than selfed seeds, suggesting that mating system has an overriding effect in influencing fitness. In light of the selection on emergence date quantified in a previous study, seed weight, emergence date, and mating system may be functioning as a cluster of characters on which selection acts jointly in this species.     

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     

Patterns in Size,Sex Ratio and Time at Emergence in a South Swedish Population of Sympetrum sanguineum (Odonata)

Differences between sexes in life history patterns of Sympetrum sanguineum were studied in a small pond in southern Sweden by means of exuviae and adult sampling. Emergence occurred from 4 to 28 July, and mean emergence date was 10 July for both males and females. The sex ratio at emergence (53% females) did not differ from 1:1, but significantly more females emerged during the first 5 days of the emergence period. Size of emerging individuals (immatures) decreased as season progressed and males emerged at a larger size than females. While immature males were heavier than immature females, no such difference was found in mature individuals. We suggest that the sexual differences in size and emergence patterns observed are the result of different optimisation by males and females with respect to the growth-mortality risk trade-off in the larval and adult stages.     

Male-male competition and mating success in the orb-web spider,Nephila clavata,with reference to temporal factors

Seasonal occurrence patterns of adults of both sexes, intensity of male-male interactions, and mating success in the spider,Nephila clavata, were examined in the field. Adult males began to attend female webs about 2 weeks before female maturation. Large adult males were abundant in the early breeding season, but small males increased later in the season. From the distribution of males among female webs and size relationship of males within a web, male-male interactions seemed to be more intense when most females were still subadult. This was verified by a field experiment in which males were artificially introduced to female webs that were attended by other males. It was found that the probability of introduced males remaining on subadult female webs was lower than that on adult webs. As mating occurred mostly in the period shortly after the female final molt and first male sperm precedence was known in all spiders reported so far, intense male-male competition on subadult female webs seemed to be reasonable. Male longevity had an important influence on the mating success of males with just-molted females. Mating success was also affected by the relative body size of males present in a given period. Since larger males occupied the position closest to females within a web and stayed there longer, relative body size appeared to influence mating success through male-male competition. Female body size at maturation declined with time; hence, males that attained sexual maturity earlier had the advantage of mating with larger and more fecund females. Therefore, early maturation as well as larger size seem to be two important trairs influencing the reproductive success of males.     

Ejaculate production schedule and the degree of protandry in fishflies (Megaloptera: Corydalidae)

1. To examine the relationship between male–female emergence patterns and ejaculate dynamics, patterns producing sperm and seminal fluids in male internal reproductive organs, the size of a spermatophore transferred at mating and the fate of spermatophore contents moved into female storage organs were compared among the fishflies (Megaloptera: Corydalidae: Chauliodinae), Parachauliodes continentalis, P. japonicus and Neochauliodes sinensis .
2. Spermatophore contents moved into female storage organs decreased rapidly in P. japonicus and N. sinensis , but hardly at all in P. continentalis . This suggests that the females of the former two species may remate sooner than the latter species as it is known in insects that material remaining in the storage organs mechanically inhibits receptivity to mating.
3. Male P. japonicus and N. sinensis increased in internal reproductive organ mass continuously after adult eclosion, and the spermatophore size produced at the first mating increased with male age. In contrast, the internal reproductive organs of P. continentalis were relatively small and did not increase in mass after emergence. P. continentalis transferred a constantly smaller spermatophore at any copulation than the former two species.
4. Males of P. japonicus and N. sinensis emerged earlier than females, while P. continentalis showed a nearly simultaneous emergence pattern between the sexes. It seems that males of P. japonicus and N. sinensis (more polyandrous than P. continentalis ) inhibit female receptivity for a longer time period by emerging earlier and transferring larger ejaculates. In these two species, the number of sperm ejaculated at the first mating also increased with male age. The increase in sperm number by emerging earlier may be adaptive for the males owing to numerical sperm competition when the female remates.     

Protandry and female size-fecundity variation in the tropical butterfly Brassolis sophorae

Protandry (the emergence of males before females) is currently explained either as a mating strategy to maximize number of matings in the males, or a way to minimize pre-reproductive mortality in females. Models of protandry have generally ignored variation in female quality (reproductive potential). We recorded the sex ratio, female body mass, wing length and potential fecundity (number and mass of eggs) of the tropical butterfly Brassolis sophorae through the emergence period. Temporal variation in female size and fecundity correlated with male potential for acquiring mates. Females from the end of the emergence period showed lower fecundity and size. Males emerging before and close to the median date of the female emergence period had greater mating opportunities. Males emerging either very early or late were penalized by few mating opportunities, or by encounters with small, low-quality females, respectively. Received: 14 November 1997 / Accepted: 23 March 1998     

Factors affecting the duration of nest defense and reproductive lifespan of female sockeye salmon, Oncorhynchus nerka

Reproductive success of female animals is often affected by a combination of fecundity and parental care. In female salmonid fishes, acquisition of nest (redd) sites and prevention of their use by other females are critical to reproductive success. These factors are particularly important for stocks that spawn at high densities. Body size is positively correlated with fecundity and egg size, and has been hypothesized to control the outcome of intrasexual competition and longevity. We tested this hypothesis by evaluating the influences of body size, intrasexual aggression and arrival date on duration and success of redd guarding by female sockeye salmon, Oncorhynchus nerka, in a small Alaskan creek. Contrary to the hypothesis, larger females guarded their redds no longer than smaller females, and did not live as long in the stream. Aggression was not related to body size or overall longevity but was positively correlated with residence period on the redd. Females that entered the creek earlier lived longer, spent longer on their redds, and spent more time guarding their redds after spawning than females that entered the creek later. However, despite their longevity, early-arriving fish were more likely to have their redds reused by another female because they died before all the females had selected redd sites. The small average body size in this stock is consistent with weak selection for large size, and with our evidence that size provided little if any advantage in nest guarding.     

Male size and survival: the effects of male combat and bird predation in Dawson's burrowing bees, Amegilladawsoni

1. Males of Dawson's burrowing bee, Amegilla dawsoni , occur in two size classes, large majors and small minors. Major males compete aggressively for emerging females in completely exposed emergence areas, whereas minors often employ an alternative mating tactic, which involves rapid patrolling in the vegetated periphery of emergence areas.
2. Because major males wrestle violently with rivals on the ground, they experience greater wing wear and a higher risk of wing damage than minor males. In addition, males patrolling emergence areas and waiting on the ground for emerging females are more likely to be killed by predatory birds than are peripheral minors.
3. Measurements of longevity based on mark–recapture data suggest that majors are slightly shorter-lived than minor males. If male–male combat and predators do reduce the lifespan of major males relative to minors, the effect would be to decrease the lifetime mating advantage of majors relative to minors.
4. Differential mortality could therefore be a factor in the maintenance of the two forms of males in this species.     

Body size as an indicator of parasitoid quality in male and female Anagyrus kamali (Hymenoptera: Encyrtidae)

The parasitoid Anagyrus kamali Moursi was recently introduced into the Caribbean as a biological control agent against the hibiscus mealybug, Maconellicoccus hirsutus Green. In the laboratory, parasitoid size, as measured by left hind tibia length, was positively correlated with several indicators of the parasitoid's fitness: longevity, mating preference, fecundity, reproductive longevity, progeny emergence and sex-ratio. When fed ad libidum with honey drops, large male parasitoids lived significantly longer (29.1 +/- 6.5 days) than small ones (18.4 +/- 5.7 days). Large females also lived significantly longer (35.4 +/- 10 days) than small females (27.9 +/- 9.6 days). Females showed no significant mating preference between large and small males. Lifetime fecundity was positively correlated with the size of adult females and ranged from 37 +/- 21 eggs for small females to 96 +/- 43 eggs for large ones. The reproductive longevity, daily oviposition rate, and number of progeny were also higher among large parasitoids. The sex ratio of progeny from small female parasitoids was higher (0.76 +/- 0.24) than that of large individuals (0.47 +/- 0.18).     

Body size, age and paternity in common brushtail possums (Trichosurus vulpecula)

Sexual selection should produce sexual size dimorphism in species where larger members of one sex obtain disproportionately more matings. Recent theory suggests that the degree of sexual size dimorphism depends on physical and temporal constraints involving the operational sex ratio, the potential reproductive rate and the trade-off between current reproductive effort and residual reproductive value. As part of a large-scale experiment on dispersal, we investigated the mating system of common brushtail possums inhabiting old-growth Eucalyptus forest in Australia. Paternity was assigned to 20 of 28 pouch-young (maternity known) genotyped at six microsatellite loci. Male mating success was strongly related to body size and age; male body weight and age being highly correlated. Despite disproportionate mating success favouring larger males, sexual size dimorphism was only apparent among older animals. Trapping and telemetry indicated that the operational sex ratio was effectively 1 : 1 and the potential reproductive rate of males was at most four times that of females. Being larger appeared to entail significant survival costs because males 'died-off' at the age at which sexual size dimorphism became apparent (8-9 years). Male and female home ranges were the same size and males appeared to be as sedentary as females. Moreover, longevity appears to be only slightly less important to male reproductive success than it is to females. It is suggested that a sedentary lifestyle and longevity are the key elements constraining selection for greater sexual size dimorphism in this 'model' medium-sized Australian marsupial herbivore.     

Effect of Adult Feeding on Male Mating Behaviour in the Butterfly, <Emphasis Type="Italic">Bicyclus anynana</Emphasis> (Lepidoptera: Nymphalidae)

Many species of lepidopterans supplement their nectar diet with foods rich in nitrogen and minerals, which are present only in trace amounts in nectar. We examined the effect of adult diet on mating behaviour and spermatophore characteristics in male Bicyclus anynana (Butler, 1879) butterflies, which feed on rotten fruits as adults. We found little effect of adult diet on male reproduction in terms of mating rate and sperm production, although males fed on fruit produced larger spermatophores on their first mating compared to males fed sugar only. We also examined how males allocate sperm across matings. Males ejaculate larger spermatophores during their first mating, and produce spermatophores containing decreasingly fewer non-fertile sperm with number of matings performed. Males that produced more non-fertile sperm on their first mating had reduced lifespan possibly indicating a trade-off between sperm production and adult longevity. It is suggested that adult diet has little affect on male ejaculate production and males feed on fruit to supplement their energetic carbon requirements.     

Reproductive performance and longevity of female European corn borer,Ostrinia nubilalis: effects of multiple mating,delay in mating,and adult feeding

In a recent study on the pheromone-mating disruption of the European corn borer, Ostrinia nubilalis (Lepidoptera: Crambidae), we recorded a significant reduction in mating frequency, as well as a marked delay in mating in feral females captured in disruptant-treated fields. In order to be able to accurately interpret the results in terms of effective population control, the current study was undertaken on the effects of multiple matings and a delay in mating on reproductive performance. Female O. nubilalis that mated at least twice had significantly higher fecundity and fertility, compared with once-mated females. In addition, multiple-mated females deposited a significantly larger portion of their egg complement, relative to single-mated or unmated females. Females that experienced a 3-day delay in mating showed a significant reduction in fecundity compared with females that mated soon after emergence. A 1-week delay in mating resulted in a further reduction in fecundity and a near zero fertility. The effect of sugar feeding on reproduction was not significant. In general, unmated females lived longer than mated females, and sugar-fed mated females had a higher longevity than water-fed mated females.     

柳毒蛾繁殖生物学的初步观察

【目的】为了明确柳毒蛾Leucoma salicis(Linnaeus)交配的日节律高峰,温度和不同交配持续时间处理对成虫寿命、产卵量和孵化率等繁殖生物学的影响。【方法】将新羽化的柳毒蛾成虫置于养虫笼中,观察交配的日节律高峰,并统计不同温度和不同交配持续时间处理下的成虫寿命、产卵量和孵化率。【结果】成虫在羽化当晚的后半夜凌晨开始交尾,次日晚上开始产卵。成虫交配集中在羽化翌日凌晨3:00—5:00之间,高峰为4:00。产卵高峰都出现在2日龄成虫,但是,25℃下成虫交配持续时间(9.2 h)显著短于28℃(11.8 h)。交配持续时间为30、60和300 min的处理,雌成虫平均寿命显著长于对照(对照9.2 h),雄虫仅60 min的处理显著长于对照。同时,极短的交配持续时间(30 min)显著降低雌虫的产卵量和孵化率。【结论】试验明确了成虫交配的日节律高峰,在适宜的温度范围内(25~28℃),雌雄成虫的寿命、单雌总产卵量无显著差异,交配持续时间明显影响成虫寿命、产卵量和卵孵化率。     

MEASURING SELECTION ON A POPULATION OF DAMSELFLIES WITH A MANIPULATED PHENOTYPE

The estimation of the relationship between phenotype and fitness in natural populations is constrained by the distribution of phenotypes available for selection to act on. Because selection is blind to the underlying genotype, a more variable phenotypic distribution created by using environmental effects can be used to enhance the power of a selection study. I measured selection on a population of adult damselflies (Enallagma boreale) whose phenotype had been modified by raising the larvae under various levels of food availability and density. Selection on body size (combination of skeletal and mass at emergence) and date of emergence was estimated in two consecutive episodes. The first episode was survival from emergence to sexual maturity and the second was reproductive success after attaining sexual maturity. Female survival to sexual maturity was lower, and therefore opportunity for selection greater, than males in both years. Opportunity for selection due to reproductive success was greater for males. The total opportunity for selection was greater for males one year and for females the other. Survival to sexual maturity was related to mass gain between emergence and sexual maturity. Females gained more mass and survived less well than males in both years but there was no linear relationship between size at emergence and survival for females in either year. However, females in the tails of the phenotype distribution were less likely to survive than those near the mean. In contrast, small males consistently gained more mass than large males and survived less well in one year. There was significant selection on timing of emergence in both years, but the direction of selection changed due to differences in weather; early emerging females were more successful one year and late emerging males and females the other. The number of clutches laid by females was independent of body size. Because the resources used to produce eggs are acquired after emergence and this was independent of size at emergence, female fitness did not increase with size. Small males may have had lower survival to sexual maturity but they had higher mating success than large males. Resources acquired prior to sexual maturity are essential for reproductive success and may in some species alter their success in inter- and intrasexual competition. Therefore, ignoring the mortality associated with resource acquisition will give an incomplete and potentially misleading picture of selection on the phenotype.     

Niche partitioning at emergence of two sympatric top-predator dragonflies,Anax imperator and A. parthenope (Odonata: Aeshnidae)

In natural communities, closely related species are phenotypically similar but usually spatially and/or temporally isolated. In odonates, interspecific competition occurs not only at the larval or adult stage but also during emergence. We investigated the emergence of two sympatric Anax species, focusing on the temporal pattern, vertical stratification, and body size trend over time. Anax imperator started to emerge two weeks earlier than A. parthenope but most of the emergence season overlapped. Both species showed an asynchronous emergence and the median emergence date was 10.3 days earlier in A. imperator. Sex ratio at emergence was not significantly different from 1:1. Body size of both species increased significantly over time, which contrasts many previous studies. The height of exuvia fixation was not significantly different between species but the larger species A. parthenope selected longer supports.     

Sexual selection on male development time in the parasitoid wasp Nasonia vitripennis

Mating systems are shaped by a species' ecology, which sets the stage for sexual selection. Males of the gregarious parasitoid wasp Nasonia vitripennis compete to mate virgin females at the natal site, before females disperse. Males could increase their fitness by being larger and monopolizing female emergence sites or by emerging earlier pre-empting access to females. We consider sexual selection on male body size and development time in Nasonia, and a potential trade-off between the two traits. We explored sex-specific patterns of larval and pupal development, finding that smaller wasps developed slower than their host-mates. Using competition experiments between brothers, we found that earlier eclosing males mated more females independently of absolute and relative body size. Our data explain the lack of relationship between fitness and body size in male Nasonia and reinforce the importance of protandry in mating systems where access to mates is time-limited.     

Biometry and biology of Constempellina brevicosta (Chironomidae) in a subarctic lake

Grimås, U. and Wiederholm, T. 1979. Biometry and biology of Constempellina brevicosta (Chironomidae) in a subarctic lake. – Holarct. Ecol. 2: 119-124. Constempellina brevicosta Edw. made up about 50% of the chironomids emerging from the littoral of Lake Blåsjön. The lake is impounded for hydroelectrical purposes. Constempellina was less abundant at an earlier, smaller amplitude of water level fluctuations in the same lake and much less abundant in a nearby natural lake. The species is able to survive in a frozen substratum on ice-covered bottoms. Records of early life stages and emergence data indicated a one-year life cycle with peak emergence from the littoral zone occurring in mid July. Statistical comparisons were made of size characteristics with respect to time and site of emergence and swarming. Swarming individuals were found to be significantly larger than emerging ones as measured in length of body, wing, tibia, and tarsi. Individuals swarming from mid July to August were successively smaller in all characters except basal antennal segments. Individuals swarming in June were smaller than those occurring somewhat later. The changes in size seem to reflect differences in larval habitat, with early summer material emanating from areas exposed to winter freezing. Males swarming at different sites at the same date were similar in all respects except for body size. Individuals emerging from different depths within the littoral zone at a single date were different in most respects, those from more shallow areas being smaller. Linear regression of swarm material from different dates showed a positive correlation for most characters. The correlations were particularly strong, and applied to all characters, when the early summer material was excluded. Mean AR values were successively lower throughout the season and positively correlated with size. Mean LR values were slightly higher in early summer than later. The LR values varied independantly of size. AR and LR values in swarm material varied between extremes for single individuals which were usually within 20% of the arithmetic mean, or 0.92–1.36 for AR and 0.78–1.06 for LR. Confidence limits for population estimates were within 0.04 units of the means.     

Relationship between male head size and mating opportunity in the harem-defence, polygynous tree weta

The most distinguishing feature of the tree weta genus Hemideina (Orthoptera: Anostostomatidae) is their cephalic weaponry, which is thought to be the result of sexual selection on males to aggressively defend groups of reproductive females. Mountain stone weta H. maori is a tree weta that shelters in cavities under flat rocks on rocky outcrops in the alpine region of the South Island. The main objectives of this study were to determine whether males with larger heads have access to greater numbers of females, and whether head size has an effect on male survival and longevity. Males with larger heads associated with larger groups of females than males with smaller heads. Male head size only accounted for 11% of the variation in mating opportunity when all rocks with females were considered, but explained 36% of the variation when only a few specific rocks that had large numbers of females were taken into account. The lower recapture rates of males in general and of smallheaded males in particular, further suggested that small males intermittently retreat to small cracks or cavities within tor columns, where there are unlikely to be large female groups. Thus, larger males had access to more females than smaller males. Moreover, larger males had no detectable disadvantage in terms of daily survival and longevity. This study provides strong evidence that larger male tree weta do associate with larger harems in the wild, however, questions relating to male weaponry size and mating success will become clearer only through paternity testing of weta under natural conditions.     

The relation between male body size, fighting, and mating success in Dawson's burrowing bee, Amegilla dawsoni (Apidae, Apinae, Anthophorini)

Males of the bee Amegilla dawsoni (Anthophorini) vary greatly in size, with some of the largest individuals as large as the largest females, a rare phenomenon in insects. The occurrence of unusually large males appears to be the product of sexual selection for fighting ability. As predicted from this hypothesis: (1) males regularly competed aggressively to be in the best position to mount sexually receptive, virgin females as they emerged from the ground; (2) larger males usually won fights for potential mates, as demonstrated by the fact that males able to defend sites with an emerging female were larger on average than males they kept at bay; (3) the fighting advantage of large males translated into greater mating success. Males captured while mounted on a female were significantly larger on average than randomly captured matesearching males in two of three populations sampled in 1993. Moreover, males known to mate more than once were consistently larger than single-mating males in the 10 samples taken from four populations examined in 1994. Thus, a large male mating advantage applies across years and among populations, making it potentially advantageous for females of Dawson's burrowing bees to produce large, superior fighting sons about the same size as their daughters.