Genetic differentiation as a result of adaptation to the phenologies of individual host trees in the galling aphid Kaltenbachiella japonica

Abstract.

• 1 The adaptation of the non-migratory galling aphid Kaltenbachiella japonica (Matsumura) to the budburst phenologies of individual host trees (Ulmus davidiana var. japonica Nakai) was investigated. There was a large variation in budburst time between individual host trees. We tested a hypothesis that aphid populations on respective host trees are genetically differentiated through adaptation to the budburst phenologies of host trees.
• 2 There was significant correlation between the budburst time of eight host trees in two successive years.
• 3 Tree-associated populations differed significantly in egg-hatching time, and the mean hatching time was significantly correlated with the mean budburst time of respective host trees.
• 4 Mating was made between male and female sexuales of the same clone (i.e. self-mating) to obtain selfed eggs. Hatching patterns of selfed eggs showed that there was a substantial amount of genetic variance in hatching time between clones (galls). Nested ANOVA demonstrated that the between-tree component contributed more to the phenotypic variance than the within-tree or within-gall components.
• 5 Reciprocal crosses between males and females of different clones furthermore demonstrated significant differences in hatching time between cross combinations, but no significant differences between the two reciprocals within combinations. This result suggests that there are no maternal effects for the timing of egg hatch and that the differences between selfed lines are attributable to genetic variance.
• 6 The fine-scale adaptation hypothesis was supported by egg-hatching experiments, which further suggest that budburst phenology varying between individual trees is acting as intense selective pressure on the egg-hatching time of associated insects.

     

Life expectancy,maximum longevity and lifetime reproductive success in female Thornicroft's giraffe in Zambia

Gestation and longevity scale with body mass across taxa, yet within size dimorphic taxa, males tend to have reduced lifespans compared with females. Testing life history models, and accounting for sex differences in longevity, requires obtaining accurate longitudinal data from wild populations. We provide the first report describing key life history parameters from a long‐term study of giraffes in Africa. We followed a population of Thornicroft's giraffe (Giraffa camelopardalis thornicrofti) in Zambia for over 40 years. Maximum longevity among females was approximately 28 years, with lifespan accounting for 81% of the variance in lifetime reproductive success. Average adult female life expectancy was no different than average adult male life expectancy. However, the breeding lifespan of males was about half that of females, while maximum lifespan of males was 75% that of females. Our findings support the suggestion that sex differences in maximum lifespan arise from stronger selection for lengthy lives in females than in males. Among females, longer lives are associated with greater reproductive output.     

Territoriality and fighting in a colonial thrips, Hoplothrips pedicularius, and sexual dimorphism in Thysanoptera

ABSTRACT.

• 1 Hoplothrips pedicularius (Haliday) (Thysanoptera: Phlaeothripidae), a tubuliferan thrips in which males possess greatly enlarged forelegs, lives in colonies on Stereum fungus.
• 2 Females oviposit onto communal egg masses, and males fight by grasping and stabbing with their forelegs in territorial defence of oviposition areas. Prolonged escalated fights occur between males who are of similar size.
• 3 Larger males usually win fights and become dominant at the oviposition area. Dominant males secure 80% of matings, and mate most frequently during oviposition periods, with an ovipositing female.
• 4 Smaller, subordinate males avoid fights and attempt to 'sneak’copulations. However, they occasionally challenge the dominant male. Challenges tend to follow copulations by the subordinate male and occur more frequently between males who are of similar size.
• 5 Subordinate males who eventually leave the oviposition area are larger than those who remain, have frequently challenged the dominant male, and have more frequently been stabbed.
• 6 Sexual dimorphism in thrips is associated with gregariousness, claustral habitats, female-biased sex ratios, and male winglessness. In thrips genera in which males exhibit foreleg armature, males are larger relative to females. The ecological circumstances promoting sexual dimorphism and male fighting in spatially-structured populations are discussed.

     

Sexual selection did not contribute to the evolution of male lifespan under curtailed age at reproduction in a seed beetle

1. Sexual selection is a powerful evolutionary force that is hypothesised to play an important role in the evolution of lifespan. Here we test for the potential contribution of sexual selection to the rapid evolution of male lifespan in replicated laboratory populations of the seed beetle, Callosobruchus maculatus. 2. For 35 generations, newly hatched virgin male beetles from eight different populations were allowed to mate for 24 h and then discarded. Sexual selection was removed in half of these populations by enforcing random monogamy. 3. Classic theory predicts that because of sexual competition, males from sexually selected lines would have higher age‐specific mortality rates and shorter lifespan than males from monogamous lines. 4. Alternatively, condition‐dependent sexual selection may also favour genes that have positive pleiotropic effects on lifespan and ageing. 5. Males from all eight populations evolved shorter lifespans compared with the source population. However, there was no difference in lifespan between males from populations with or without sexual selection. Thus, sexual selection did not contribute to the evolution of male lifespan despite the fact that such evolution did occur in our study populations.     

Multiple mating and its effect on the reproductive success of female Epiphyas postvittana (Lepidoptera: Tortricidae)

Abstract.

• 1 Multiple mating and its effect on reproductive performance of female Epiphyas postvittana (Walker) moths were studied under controlled conditions.
• 2 The age at which the moths mated for the first time ranged from the first to the tenth day after emergence, but 71% of first matings were during the first 3 days.
• 3 The majority (63%) of females had one or two spermatophores in the bursa copulatrix. Some (24%) were found with three to five spermatophores, whereas no successful mating occurred among 13% of individuals. The number of matings was partly dependent on the number of mates available to the female. Between the range of sex ratios of one male to one female and four males to one female maximal mating success occurred at the ratio of three males to one female.
• 4 Virgin females were capable of egg-laying, but mating stimulated and accelerated oviposition. Mated individuals laid twice as many eggs as unmated ones.
• 5 The level of copulatory activity did not influence the longevity of females irrespective of the number of males available to them.
• 6 Sex ratios with greater than one male to a female improved the reproductive success by marginally increasing fecundity and fertility.
• 7 It is concluded that multiple mating would enhance population growth, and is of particular benefit to populations with a preponderance of females, as is known to occur naturally in this species.

     

Egg fertilisation in a freshwater mussel: effects of distance,flow and male density

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Lifetime patterns of pairing success in male Ortolan Buntings Emberiza hortulana

Analyses of lifetime fitness in birds are typically based on estimates of breeding success, in particular the number of offspring fledged. Small and isolated bird populations often have a male‐skewed adult sex ratio, so that male lifetime productivity depends to a large degree on pairing success, but few studies have focused on patterns of lifetime pairing success. The Norwegian population of Ortolan Buntings Emberiza hortulana is strongly male‐skewed, such that in any year about half of all males are unpaired. Pairing success of first‐year males (16–44%) was significantly lower than for older males (52–89%). Lifetime pairing success was correlated with lifespan and was strongly skewed, with a majority of males being paired only once or never, and only 11% paired three or more times despite a stable lifetime annual survival rate of 63%. Males that were paired in one year were more likely to be paired the next year than males that were unpaired in the previous year. The shortage of females caused even the older males to have a substantial probability of becoming unpaired, and 49% of long‐lived males (known as adults for at least 4 years) were unpaired after years in which they were paired. Pairing success in the Ortolan Bunting therefore follows similar age‐related and lifetime patterns in breeding success documented in other species. However, even the older males ran a high risk of not being paired, contrasting with earlier distinctions between pre‐breeding and breeding lifespans. I discuss the importance of knowledge of pairing success for the management of endangered and declining populations.     

Variance in male reproductive success and sexual size dimorphism in pinnipeds: testing an assumption of sexual selection theory

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Microdot technology for individual marking of small arthropods

• 1 Individual mark–release–recapture is an important method for gathering data on insect movement, although it is limited by the constraints of tagging small insects with individual information.
• 2 Microdots, originally developed for covert security applications, are small polymer discs (diameter 0.5 mm) bearing up to 26 characters of information and have the potential as an alternative to the larger bee tags. In the present study, we test microdots for the individual marking of a 9‐mm parasitoid wasp.
• 3 We individually marked 505 wasps. The recapture rate was 24% of individuals over 189 recapture events, for which 84% retained legible microdot labels. Movement was in the range 0–161 m with a mean displacement 21.2 ± 2.7 m. A captive survival experiment showed no difference in lifespan between marked and unmarked wasps.
• 4 The present study shows that microdots can provide an effective, durable, low‐cost method for individually tagging small insects. The technique offers new opportunities by greatly expanding the capability for individually marking small insects, shifting the minimum size below that of bee tags, which is the only other manufactured option for individualized miniature marking.

     

Nest-site size as a short-term constraint on the reproductive success of paternal fishes

Synopsis Because female signal blennies, Emblemaria hypacanthus (Pisces: Chaenopsidae), exhibited a preference for the larger of two males in laboratory mate-choice experiments, male reproductive success was predicted to be positively correlated with male size in field populations. This prediction was met at one field site, but not a second where shelter size, rather than male size, was the primary correlate of male reproductive success. This finding appeared to be the consequence of the relatively small size of shelters (vacant gastropod shells) at the second site. At this site, significantly more males had their shelters filled with eggs and variance in male reproductive success was lower than at the first site. Limited area for deposition of eggs is potentially an important constraint on the short-term reproductive success of paternal males of shelter- or crevice-spawning fishes.     

Mating system of Bracon hebetor (Hymenoptera: Braconidae)

Abstract.

• 1 We report on the mating system of a field population of the parasitic wasp, Bracon hebetor, on a corn pile infested by the Indian meal moth, Plodia interpunctella. We demonstrate that the mating system is based upon male scramble competition polygyny with male aggregations on high places on the corn.
• 2 The sex ratio among adults was greater than 80% males on the surface of the corn, whereas below the surface the sex ratio was less than 45%. Males actively courted females on the surface, but there were no aggressive interactions among males during courtship or mating.
• 3 Approximately 20% of the females found on the surface of the corn had no sperm in their spermathecae, regardless of age, but the numbers of unmated females decreased later during the day.
• 4 In laboratory studies we showed that females from this population oviposit a female biassed sex ratio, and that only 14% of females were mated before dispersing from their place of emergence.
• 5 Thus sib-mating is unlikely in this gregarious parasitoid. This outcrossing mating system probably arose because of severe inbreeding depression that B.hebetor suffers via a sex locus: diploids that are heterozygous at the sex locus develop into females, but homozygous diploids are male and are generally inviable. The female biassed sex ratio may have evolved in B. hebetor in response to males being the more expensive sex, females dispersing more frequently from the population than males, or a fraction of females remaining unmated in the population.

     

Persistent size variation in the anthophorine bee Centris pallida (Apidae) despite a large male mating advantage

Abstract.

• 1 Despite apparent directional sexual selection in favour of large body size, males of the anthophorine bee Centris pallida remain highly variable in body size.
• 2 One possible cause of persistent size variation among males is geographic variation in the extent of the large male mating advantage. However, a study of a population in an area not previously investigated revealed that the large male mating advantage was as strong here as it has been elsewhere in other years.
• 3 Although the reproductive benefits of being large were consistent in populations separated spatially and temporally, the intensity of bird predation on mate-searching males varied greatly between locations.
• 4 The bee-killing birds focused exclusively on bees which were digging down to meet emerging females or fighting on the ground, never on flying males. Males which were collected on the ground by hand (to simulate avian predation) were significantly larger on average than flying males collected by sweep netting.
• 5 Therefore, in some location in some years, sexual selection in favour of large body size may be opposed by natural selection exerted by predators, perhaps contributing to the maintenance of size variation in this bee.

     

Acarbose, 17‐α‐estradiol,and nordihydroguaiaretic acid extend mouse lifespan preferentially in males

Four agents — acarbose (ACA), 17‐α‐estradiol (EST), nordihydroguaiaretic acid (NDGA), and methylene blue (MB) — were evaluated for lifespan effects in genetically heterogeneous mice tested at three sites. Acarbose increased male median lifespan by 22% (P < 0.0001), but increased female median lifespan by only 5% (P = 0.01). This sexual dimorphism in ACA lifespan effect could not be explained by differences in effects on weight. Maximum lifespan (90th percentile) increased 11% (P < 0.001) in males and 9% (P = 0.001) in females. EST increased male median lifespan by 12% (P = 0.002), but did not lead to a significant effect on maximum lifespan. The benefits of EST were much stronger at one test site than at the other two and were not explained by effects on body weight. EST did not alter female lifespan. NDGA increased male median lifespan by 8–10% at three different doses, with P‐values ranging from 0.04 to 0.005. Females did not show a lifespan benefit from NDGA, even at a dose that produced blood levels similar to those in males, which did show a strong lifespan benefit. MB did not alter median lifespan of males or females, but did produce a small, statistically significant (6%, P = 0.004) increase in female maximum lifespan. These results provide new pharmacological models for exploring processes that regulate the timing of aging and late‐life diseases, and in particular for testing hypotheses about sexual dimorphism in aging and health.     

Distribution of male yellow dungflies around ovipasition sites: the effect of body size

Abstract.

• 1 Spatial and temporal variation in body size of yellow dungflies, Scatophaga stercoraria, gathering on and around cow droppings was studied in an Icelandic population in order to elucidate the effect of male and female size on male mating tactics.
• 2 Males copulating on droppings were on average larger than males copulating in the grass, but of similar size to males guarding ovipositing females. Males searching on droppings were smaller than males copulating or guarding females on droppings but larger than males copulating in the grass. No such differences were found in female size.
• 3 Resource-holding power of males (RHP, i.e. male: female size ratio) differed between the three mating groups and was highest for males on the droppings. Size and RHP clearly affect the tactics of copulating males. Males with low RHP tend to copulate in the grass in spite of the cost of longer copulation duration. We argue that this is caused by risk of takeovers from large searching males.
• 4 There was no change in male size with the age of individual droppings. Contrary to what might be expected, large searching males are not predominantly found at fresh droppings when the probability of catching unpaired females is highest. We suggest instead that good prospects in taking females over from other males must make the strategy to search for females on older droppings profitable.
• 5 RHP did not change with age of dropping in the three mating groups. The size of ovipositing females increased with age of dropping, probably reflecting longer copulation and egg-laying times of large females.
• 6 We found an overall positive relationship between sizes of male and female partners. This correlation was highly significant for copulating pairs in the grass. This is probably a consequence of males with low RHP copulating in the grass and fights in which larger males take over females from smaller males. A weaker, but significant, correlation was found amongst ovipositing pairs. This must be due to take-over effects. No size correlation was found for pairs copulating on droppings.

     

Changes in life-cycle strategies of Carabus problematicus over a range of altitudes in Northern England

ABSTRACT.

• 1 Mandible tip length has been used to estimate the age of individual C.problematicus Herbst caught over an altitude range of more than 700 m in northern England.
• 2 At 100 m the great majority of females laid eggs in the summer of their emergence as adults. The female life-cycle is predominantly annual and 24% only of the egg-bearing individuals were in their second year.
• 3 Above 250 m, most females did not reproduce until the summer of the year following emergence, giving a biennial life-cycle. 96% of egg-bearing females caught above 830 m were in their second year.
• 4 All the males caught during the breeding season at 100 m had emerged within that calendar year and it is concluded that the male life-cycle is annual at this altitude.
• 5 Above 250 m, 83% of the males caught during the breeding season were in their first calendar year, suggesting that recently emerged males may inseminate second year females and also that the male life-cycle is predominantly annual over the whole altitude range studied.
• 6 At the higher temperatures of the lowland site females not only produce eggs in the year of emergence, they also produce more eggs per individual than at the higher sites. Egg production depends on food intake which involves mandible wear and individuals at the lowland site have significantly higher rate of mandible wear than at the sites above 250 m.

     

Recapture studies of the harvester ant, Pogonomyrmex owyheei Cole, using a fluorescent marking technique

Abstract.

• 1 Mark—recapture sampling must be stratified because populations of foragers and defenders are partitioned by trunk trails and order of emergence respectively.
• 2 Foragers and defenders form overlapping subsets of the total colony population, each of which is correlated with total colony population size.
• 3 Foragers and defenders have an average life expectancy of approximately 2 weeks.
• 4 The fluorescent marking procedure did not significantly affect harvester ant mortality and only temporarily affected their behaviour.
• 5 Combinations and mixtures of fluorescent ink allow at least eight groups in a colony to be distinctly marked for periods exceeding 4 months.

     

Lifetime mating success in the damselfly Coenagrion puella

Lifetime mating success of male azure damselflies (Coenagrion puella) was measured in a natural population. The major determinant of mating success is the number of days a male spends at the breeding site, which is mostly determined by a male's adult lifespan. Long-lived males have a higher mating rate than short-lived males, and daily mating rate increases with age up to 6 days, then falls. Large males live longer, but have a lower daily mating rate than small males. These effects of size are very weak, accounting for no more than 2% of the daily variance in mating success. The only overall effect of size on lifetime mating success is that males at both extremes of the size distribution are more likely to fail to mate. Chance differences in the number of females encountered are sufficient to account for the remaining variance in mating success. The weather is also shown to have a major effect on mating success. We draw attention to the ways in which it may be misleading to draw conclusions about the action of sexual selection from studies of daily, rather than lifetime, reproductive success. We provide evidence to support the view that variance in male reproductive success is neither evidence for sexual selection, nor a measure of its intensity.     

Marking through molts: An evaluation of visible implant elastomer to permanently mark individuals in a lower termite species

1. Advances in individual marking methods have facilitated detailed studies of animal populations and behavior as they allow tracking of individuals through time and space. Hemimetabolous insects, representing a wide range of commonly used model organisms, present a unique challenge to individual marking as they are not only generally small‐bodied, but also molt throughout development, meaning that traditional surface marks are not persistent.
2. Visible implant elastomer (VIE) offers a potential solution as small amounts of the inert polymer can be implanted under the skin or cuticle of an animal. VIE has proved useful for individually marking fish, crustaceans, and amphibians in both field and laboratory studies and has recently been successfully trialed in laboratory populations of worms and fly larvae. We trialed VIE in the single‐piece nesting termite Zootermopsis angusticollis, a small hemimetabolous insect.
3. We found that there was no effect of VIE on survival and that marks persisted following molting. However, we found some evidence that marked termites performed less allogrooming and trophallaxis than controls, although effect sizes were very small.
4. Our study suggests that VIE is an effective technique for marking small hemimetabolous insects like termites but we advocate that caution is applied, particularly when behavioral observation is important.

     

Is the Iberian lacewing Chrysopa regalis a semivoltine species?

ABSTRACT.

• 1 Adults of the lacewing Chrysopa regalis Navás were caught in north Spain, Huesca province, Aragon.
• 2 Their progeny reared in the laboratory under short- and long-day light conditions at 20°C, entered a long diapause as prepupae within the cocoon.
• 3 Transferred outdoors after spinning up, only a few (12%) became active again in the following spring, whereas the rest remained in diapause for one more year and waited for the end of the second spring to resume their morphogenetic development. Thus most of the studied strain exhibited a 2–year life cycle. This semivoltine strategy is new to chrysopid biology.
• 4 The predaceous larval phase did not exceed 3% of the total individual lifespan, though the duration of the free-living larval instars averaged 19.9±1.1 (SD) days.
• 5 During the extended diapause, weight loss was very small, no more than 6.6% of the initial weight, 16.9±2.7 (SD) mg, at the end of diapause, and 8.8% at the time of pupal ecdysis.

     

The calling behaviour and spatial distribution of male bushcrickets (Sciarasaga quadrata) and their relationship to parasitism by acoustically orienting tachinid flies

Abstract.

• 1 This paper examines the calling behaviour and spatial distribution of male Sciarasaga quadrata Rentz (Orthoptera: Tettigoniidae), a bushcricket that is subject to attack by an acoustically orienting parasitoid fly, Homotrixa sp. (Diptera: Tachinidae: Ormiini).
• 2 Checks on calling activity in populations of S.quadrata confirmed that calling began 2–3 h before sunset and continued well beyond midnight. Calling activity was not restricted by temperature with males calling over air temperatures of 10.6–24.2°C.
• 3 Nearest-neighbour analyses, within the sampled areas, revealed that the spacing between calling males was random and the minimum distance between calling males was 3.74 m. Mean distances between calling males varied between 9.2 m and 23.0 m and significantly changed as male density, which peaked at 0.36 calling males per 100 m², declined over the calling season.
• 4 Males showed no preference for any one plant species, with their distribution across bushes not significantly different to the frequency of the plants within the habitat. The perch height of calling males was on average half way up the height of a bush and was significantly influenced by the height of the bush. Perch height was not significantly influenced by proximity to calling males or by whether or not males were parasitized.
• 5 Site fidelity of males was low with only 0–10% of bushes occupied by calling males over successive nights. Males, though flightless, moved on average 6.70 m and up to 26.56 m per night.
• 6 No evidence was found for the use of aggregation in S.quadrata as a primary defence against ormiine attack. Commencing calling prior to sunset, frequent movement, and a lack of association with any particular plant species, although possibly relevant to ormiine attack, could also be explained in terms of other activities such as male-male interactions and mating behaviour.