Male reproductive polymorphism and form-specific habitat utilization of the damselflyMnais pruinosa (Zygoptera: Calopterygidae)

Habitat utilization patterns were studied in damselfly males,Mnais pruinosa, which have two male forms with different reproductive behaviors. The ‘esakii’ (orange-winged males) were territorial around oviposition sites, while the ‘strigata’ (hyaline-winged males) were non-territorial, often sneaking into theesakii's territory or loitering on the foliage of vegetation along stream banks. The place in the stream in the study area where females frequently appeared was covered by reeds and had abundant oviposition sites. It was difficult for the territorialesakii to stay there because the crowded reeds prevented them from defending their territory and discovering the females. Furthermore, there was competition for the limited territorial space with another species,Mnais nawai. Strigata males concentrated in this place in direct proportion to the number of females. Females frequently mated withstrigata males and probably deposited eggs fertilized bystrigata sperm rather thanesakii sperm. The density ofstrigata was higher than that ofesakii in this study area. If the average reproductive success ofesakii andstrigata males is equal, this may indicate that the equilibrious point between the two male forms is biased towardstrigata.     

Mating tactics and male wing dimorphism in the damselfly,Mnais pruinosa costalis selys (Odonata: Calopterygidae)

Males of the damselfly,Mnais pruinosa costalis, exhibit wing color dimorphism: one form has orange wings, and the other hyaline wings which resemble female wings. The former is usually territorial and the latter uses sneaky mate securing tactics. When orange-winged males failed to establish territory, they became floaters that day. Hyaline-winged males perched around their territories and often, formed in tandem without any apparent courtship behavior when they found females. Their copulation frequency was higher and copulation duration longer than those of territorial males. A few females oviposited without remating. Total oviposition duration of females with which a hyaline-winged male mated was more than 32 min per male on average in a day Females that copulated with hyaline-winged males often remated with orange-winged residents before oviposition. Total duration of oviposition bouts of females after mating with floaters was short (15 min), while that with territorial residents was long (66 min). As a result, total oviposition duration of females with which an orange-winged male mated was about 40 min in a day. The reproductive success of the hyaline-winged males may be similar to that of the orange-winged males.     

Reproductive behavior of females and its relation to the mating success of two male forms inMnais pruinosa (Zygoptera: Calopterygidae)

The behavior of females of the damselflyMnais pruinosa was observed in the breeding season. Males consisted of both territorial (esakii) and non-territorial (strigata) types in the study area. Females sometimes arrived at a stream for mating and oviposition. The staying time of females in the stream was 1–3 hours, while that of males was 5–8 hours. The proportion of the males that copulated with the females did not differ between the two male forms present in the stream. In the Calopterygidae, of which the females usually perform multiple copulation, oviposition without subsequent recopulation is considered to be advantageous for a mated male in order to avoid the risk of sperm displacement. From such a viewpoint, the time spent for oviposition was measured for females that arrived at the stream after copulation with different male forms. The ratio was 69.1: 11.5–30.9 betweenesakii andstrigata males. Assuming that the oviposition time is proportional to the number of fertilized eggs laid, this ratio would represent the relative reproductive success of the two male forms. In fact, the relative abundance of the two male forms was also biased in favor ofesakii males (61.7:38.3) in this population. The mechanism of coexistence of the two male forms is discussed in relation to their reproductive success.     

Remarkable iridescence in the hindwings of the damselfly Neurobasis chinensis chinensis (Linnaeus) (Zygoptera: Calopterygidae)

The bright green dorsal iridescence of the hindwings of Neurobasis chinensis chinensis males, very rare in Odonata, is known to play a significant role in their courtship behaviour. The mechanism responsible for such high contrast and spectrally pure colour has been investigated and found to be optical interference, producing structural colour from distinct laminations in the wing membrane cuticle. The ventral sides of these iridescent wings are dark brown in colour. In a single continuous membrane of wing cuticle, this is an effect that requires a specialized structure. It is accomplished through the presence of high optical absorption (kappa = 0.13) within two thick layers near the ventral surface of the wing, which leads to superior dorsal colour characteristics. By simultaneously fitting five sets of optical reflectivity and transmissivity spectra to theory, we were able to extract very accurate values of the complex refractive index for all three layer types present in the wing. The real parts of these are n = 1.47, 1.68 and 1.74. Although there is often similarly significant dorsal and ventral colour contrast in other structurally coloured natural systems, very few system designs comprise only a single continuous membrane.     

Synchronization of reproductive period among the two male forms and female of the damselflyMnais pruinosa selys (Zygoptera: Calopterygidae)

Ecological parameters in a population ofMnais pruinosa were investigated in a mountain stream. In the study area, there were two forms of male with regard to wing color, the orange-winged male (esakii) and the hyaline-winged male (strigata), and only one female form with hyaline wings. Emergence of adults began in late April, and the flying season ended in late June. The time after emergence was spent in maturation, and the insects began to mate when they reached maturity. Longevity of adults was 17.6 days foresakii males, 18.4 days forstrigata males and 21.9 days for females. There was little difference in emergence time, maturation period, survivorship curve and longevity among the two male forms and female. In other words, the period for reproductive activities was perfectly coincident among them. The factors influencing the synchronization of emergence were discussed.     

Variable microsatellite loci isolated from the azure damselfly,Coenagrion puella (L.) (Zygoptera; Coenagrionidae)

We isolated and characterized 10 polymorphic microsatellite loci from the azure damselfly Coenagrion puella (Zygoptera; Coenagrionidae) as part of a study assessing reproductive success and genetic structure in an isolated population of this species. Levels of genetic diversity were assessed in 50 individuals collected from Queen Elizabeth Country Park, Hampshire, UK. The number of alleles per microsatellite loci ranged from three to 22 and the observed and expected heterozygosities varied between 0.26 and 0.84 and between 0.23 and 0.91, respectively. Two loci showed significant (P < 0.05) heterozygote deficits, likely because of null (non‐amplifying) alleles; one pair of loci was in linkage disequilibrium.     

Asymmetric intraspecific competition among larvae of the damselfly Ischnura elegans (Zygoptera: Coenagrionidae)

Abstract. 1. A laboratory competition experiment is described in which the growth and development rates of larvae of the damselfly Ischnura elegans (Lind.) were measured over an entire instar.
2. Two larval instars which commonly occur together in the field were used in the experiment; they were maintained with a superabundance of prey and either larvae from the same or the larger/smaller instar.
3. Small larvae suffered increased development times and decreased size increases at the moult in the presence of large larvae but similar interference effects were not evident when these smaller larvae were in the presence of other small larvae.
4. Development time and size increases of large larvae were not significantly affected by the presence of small larvae.
5. Irrespective of the instar combinations investigated, interference effects were reduced when there were more perches available, although in only a few cases was this reduction significant.
6. The consequences of the asymmetric competition reported in the experiment for the study of lifetime reproductive success in damselflies are discussed. Late emerging adults may incur reduced reproductive success.     

Food utilization of aphidophagous hoverfly larvae (Diptera: Syrphidae, Chamaemyiidae) on herbaceous plants in an urban habitat

We examined food utilization in a community of aphidophagous hoverfly larvae (Diptera: Syrphidae and Chamaemyiidae) in open lands in an urban habitat in central Japan for 3 years. The community consisted of 17 hoverfly species feeding on 20 aphid species occurring on 14 species of dominant herbaceous plants. In terms of larval prey preference, the dominant eight species of hoverfly were categorized into three groups: a polyphagous ‘generalist’ group consisting of four species,Episyrphus balteatus, Betasyrphus serarius, Syrphus vitripennis andSphaerophoria sp.; an oligophagous ‘specialist’ group consisting of three species,Metasyrphus hakiensis, Dideoides latus andParagus hemorrhous; andLeucopis puncticornis, which showed a preference for two aphid species on the plantTorilis scabra. The prey aphids of the second group have behavioral or morphological defense mechanisms that are effective for preventing attacks by generalist hoverflies; two prey aphids are aggressive toward generalist predators and the others are protected by ant-attendance. The specialist hoverflies seem to be adapted to overcome these defense mechanisms. The prey ranges overlapped little between the generalist and the specialist groups, while those within the generalist group overlapped greatly.     

Expression of a costly, plastic secondary sexual trait is correlated with age and condition in a damselfly with two male morphs

Males of the damselfly Mnais costalis Selys (Odonata: Calopterygidae) are morphologically and behaviourally polymorphic, typically existing as clear-winged non-territorial ‘sneaks’ and orange-winged territorial ‘fighters’. The amount of orange pigment in the wing, as measured with a chromameter, varied between individuals, and decreased as the reproductive season progressed. Young individuals maintained in the laboratory on high or low nutrient diets differed in the amount of pigment that developed in the wing. Males in the high nutrient group developed darker wings faster than those in the low nutrient group. Young adults of both sexes and morphs were fed ¹⁴C-radiolabelled tryptophan or tyrosine (precursors of the pigments ommochrome and melanin, respectively). Ommochrome was restricted to the pseudopterostigma of the males of both morphs and was not present in females. The presence of tyrosine in the wing cells of orange males, but not of clear males, indicated that the orange pigment is at least partly constituted from melanin. These data show that at least some pigment levels must be maintained continuously in the wings of orange males, and that maintenance is costly as it is compromised at low nutrient levels.     

Body temperature regulation is associated with climatic and geographical variables but not wing pigmentation in two rubyspot damselflies (Odonata: Calopterygidae)

It has been proposed that wing pigmented spots function in temperature control in male calopterygids. Using two rubyspot species Hetaerina americana Fabricius and Hetaerina vulnerata Hagen in Selys, the present study investigated whether (i) wing spot size and colour‐modified aspect can predict temperature gain after a cooling event; (ii) wing spot size is related to the temperature needed to fly and how long it takes to initiate flight; and (iii) wing spot size is related to seasonality and altitude. The results obtained do not support any of these relationships. The results also indicate that H. vulnerata can achieve flight at 8 °C less than H. americana. The present study further investigates whether the species differ in their latitudinal and geographical distribution, and respond differently to bioclimatic variables. The results obtained provide support for this particular hypothesis, showing that H. vulnerata inhabits higher altitudes, and is able to tolerate colder environments compared with H. americana. Wing spots in the two Hetaerina species do not help in thermoregulation, although both species show different temperature control abilities. This difference in thermoregulatory ability may enable the species to colonize different environments and reduce interspecific competition.     

Male Reproductive Success in a Promiscuous Armoured Catfish Corydoras Aeneus (Callichthyidae)

Among a variety of fish mating systems, promiscuity with random-mating seems to be most prevalent. However, detailed studies of promiscuity have been rare due partly to the peculiar difficulty in examination of male mating and reproductive success in the random mating. Females of the armoured catfish Corydoras aeneus (no sexual dimorphism other than size of males > females) spawn 10–20 egg-clutches with multiple males at a time, but an entire egg clutch is inseminated by sperm of a single male. We studied mating system of this fish in aquarium. Males had neither mating territories nor monopolized females, never being aggressive against rival males. Evidence of female preference for certain male traits including size was not detected. Females mated a male in proportion to his relative courtship frequency among males. Courtship frequency was not related to male size, and male mating success was not different between small and large males. Clutch size and insemination rate were different neither between small and large males nor between frequently and less frequently courting males. Thus, the male reproductive success will not be related to the male size, but directly to courtship frequency, indicating the random mating in this fish. There seemed to be fecundity advantage with size in female, and the consequent sexual difference in energy allocation will be responsible to the sexual dimorphism. We also discuss the low male-GSI in this promiscuous fish in which sperm competition hardly occurred.     

Body size influences mating success of the Eucalyptus longhorned borer (Coleoptera: Cerambycidae)

Both sexes of adultPhoracantha semipunctata F. (Coleoptera: Cerambycidae) congregate on stressedEucalyptus that are the larval hosts. In a field study, 721 adultP. semipunctata captured on host trees varied considerably in body size with the largest individuals being about twice the length of the smallest. Females that were paired with a mate were similar in size to solitary females, suggesting that the probability of a female being mated was not affected by her size. However, large males had greater success than smaller males in obtaining mates. MaleP. semipunctata rely on antennal contact to locate and identify females on the larval host. Therefore, the rate at which males search for mates is a function of the area swept by their antennae per unit time. Because of their greater antennal spread, large males were able to search for females at double the rate of the smallest males. Large males also dominated in aggressive contests for females. The superior abilities of large maleP. semipunctata in both locating and defending mates account for the influence of body size on mating success.     

Space use by the Japanese fluvial sculpin, Cottus pollux, related to spatio-temporal limitations in nest resources

Space use by the Japanese fluvial sculpin, Cottus pollux, as related to nest availability was studied in a Japanese mountain stream. Males had larger home ranges than females before breeding. A measure of nest resource limitation was L < 1 and the same nest rock was used by two males successively in three cases, indicating a limited supply of suitable nest rocks for males. All males included the nest rocks in their home ranges, but the timing of nest occupation was apparently dependent on male size, suggesting the presence of male-male competition for the nest rocks. Females, on the other hand, exhibited two different patterns in space use, independent of body size: (1) they spawned in their home ranges, or (2) they spawned out of their home ranges and returned. Nest cavity area did not affect male reproductive success. Spatial separation between female home ranges and nest location was the main reason for the females' movement out of their home ranges. The limitation in the male mating phase (5.7 days on average) might also have forced the females to move out of their home range to spawn. The reason behind such temporal limitation in the male mating interval was discussed from the viewpoint of the energy cost accompanying male parental care.     

Sensory trap as the mechanism of sexual selection in a damselfly genitalic trait (Insecta: Calopterygidae)

During copulation, males of some calopterygid damselfly species displace the sperm stored in the spermatheca: the male genital appendages enter into the spermathecal ducts and physically remove sperm. In Calopteryx haemorrhoidalis, the genital appendages are too wide to penetrate the spermathecae, but males use a different mechanism in which the aedeagus stimulates the vaginal sensilla that control spermathecal sperm release. Since these sensilla are used during egg fertilization and oviposition, it was hypothesized that this function evolved before the male stimulatory ability. I investigated this using Hetaerina cruentata, a species whose position in the Calopterygidae phylogeny is more basal than Calopteryx. Given this position and having determined that males of this species are not able to displace sperm of their conspecific females during copulation, it was expected that H. cruentata females would eject sperm when stimulated with the aedeagi of C. haemorrhoidalis but not when stimulated with the aedeagi of their conspecifics. This prediction was confirmed. In order to investigate the widespread nature of this result, some other Calopteryx species-Calopteryx xanthostoma and Calopteryx virgo-were investigated. The results were similar to those of H. cruentata: conspecific males were unable to stimulate their females, but females ejected sperm when stimulated with C. haemorrhoidalis aedeagi. Morphometric analysis suggests that the mechanistic explanation for the stimulatory ability of C. haemorrhoidalis genitalia is that the aedeagal region that makes contact with the vaginal sensilla is wider in C. haemorrhoidalis than in the other species. These results suggest that the sensory "bias" shown and shared by H. cruentata, Calopteryx splendens, C. virgo, and C. haemorrhoidalis females represents an ancestral condition and that the male stimulatory ability is absent in the evolutionary history of the clade. These pieces of evidence as well as another one presented elsewhere, which indicates that C. haemorrhoidalis males vary in their stimulatory ability, constitute the three criteria for a case of sexual selection via exploitation of a female sensory bias. These results also provide support to the sensory trap hypothesis that indicates that the female bias-in this case, egg fertilization and oviposition-evolved in a context different from sexual selection. Considering that the male genital appendages responsible for physically removing spermathecal sperm in other calopterygids are present in C. haemorrhoidalis, I suggest that males were once able to displace spermathecal sperm physically. Such ability may have been later impeded by a reduction in size of the spermathecal ducts. Possibly, one of the latest events in this sequence is the male's stimulatory ability. This hypothetical series of events suggests a coevolutionary scenario in which the central actor is the sperm stored in the spermathecae.     

Age‐ and sex‐related differences in the spatial ecology of a dichromatic tropical python (Morelia viridis)

Abstract: Despite outnumbering their temperate counterparts, tropical snake species have been poorly studied. Yet, the few tropical species that have been studied show a variety of behavioural traits beyond those described in temperate species. Here we reveal both age and sexual differences in the movements of tropical green pythons (Morelia viridis: Pythonidae). We radio‐tracked 27 individuals (17 females and 10 males) for up to 18 months, locating individuals during both the day and night. The home range size for adult females (mean ± SE of 6.21 ± 1.85 ha) was correlated with snout–vent length. Neither adult males nor juveniles had a stable home range. Adult females had stable home ranges that overlapped considerably with those of other females and yellow individuals. Multiple radio‐tracked adult males passed through the territory of radio‐tracked adult females during the study. Females of all sizes were more likely to change position each day than males. There were no differences between the sexes or size categories in the distances moved in most months, although the variation in movement distances was higher in the dry season than during the wet season. In the wet season (January–March) movement distances increased and these were size‐ and sex‐related. This increased activity may be associated with mate searching. Males of M. viridis may maximize their rate of encountering mature females by roaming rather than maintaining a home range. Juvenile green pythons moved distances equal to adult snakes in most months despite their comparatively small size.     

The Race for Females: The Mating System of the Red Mason Bee, Osmia rufa (L.) (Hymenoptera: Megachilidae)

The ecology of a species strongly influences the strategies with which males and females maximize their lifetime reproductive success. When males and females do not invest equally in offspring, the sex with the higher parental investment becomes a rare resource for the other. The spatial and temporal distribution of the limiting sex forms the basis of the mating system. In nest-constructing Aculeata such as the red mason bee, Osmia rufa, females perform intensive brood care, whereas males do not invest in their offspring but instead compete for access to mates. Receptive females of this species are widely distributed and do not assemble at certain places. Therefore, territorial behavior is not an advantageous mating tactic for males, which instead search for females within individual home ranges usually centered around food plants. The unmarked or defended home ranges of different males may completely overlap. Competitive searching leads to a random distribution of matings among males that is largely independent of body size. The mating system of O. rufa can be described as scramble competition polygyny.     

Spatial distribution of mate-searching males in the damselfly,Cercion c. calamorum (Odonata: Zygoptera)

Both sexes of the coenagrionid damselflyCercion c. calamorum meet at, or near, ponds for oviposition. Spatial distribution of mate-searching males at a study pond was established with the following 2 simple and independent rules: (1) males don't go far from the roosting sites of the previous night; (2) once males reach one of the oviposition sites, the length of their stay is related to site quality. The first rule may correspond to the decrease in the number of receptive females at greater distances from the shore, and the second rule may relate to the higher predictability of female arrival at better oviposition sites. Contribution from the Laboratory of Animal Ecology, Kyoto University, No. 543.     

Interspecific mating in the Piriqueta caroliniana (Turneraceae) complex: effects of pollen load size and composition

Two taxa of Piriqueta (P. caroliniana and P. viridis) form a broad hybrid zone that extends over much of the central Florida peninsula. We used genetic markers to examine the strength of the isolation barriers between these taxa and the patterns of mating at the initial stages of hybridization. Regression models were employed to analyze the effects of pollen load size and the proportions of intra- and interspecific pollen on the frequency of first-generation (F1) hybrid formation. Overall, the postpollination mating barriers between these two taxa were relatively weak. However, there were significant effects of pollen load composition and size on the patterns of hybridization in both taxa with frequency-dependent responses to composition in both taxa. The frequency of F1 hybrid formation was generally lower than expected based on the frequency of each pollen type on the stigma for P. caroliniana recipients. The lower frequencies of F1 seeds in this taxon were apparently due to a greater competitive ability for intraspecific pollen, since hybrid seed formation decreased with increasing pollen load size. Pollen from P. caroliniana donors was also competitively superior on P. viridis recipients, leading to higher than expected frequencies of hybrid seed formation. Pollen from P. caroliniana did suffer higher rates of pollen-tube attrition than intraspecific pollen on P. viridis recipients, so the frequency of hybrid seed formation would be lower when pellen load sizes were small. In general, reproductive isolation mechanisms were stronger in P. caroliniana, suggesting that introgression should occur into P. viridis when these taxa come into close contact. Comparison of these expected patterns of mating to the distribution of hybrid genotypes in Florida provides insights into the relative roles of mating and selection in the evolution of hybrid populations of Piriqueta.     

Early comers occupy popular territories in a lycaenid butterfly,Chrysozephyrus smaragdinus (Lepidoptera: Lycaenidae)

Territorial activities of a lycaenid butterfly, Chrysozephyrus smaragdinus, were observed throughout its adult season to investigate the territorial dynamics. The territories occupied earlier in the season were abandoned later than later‐occupied territories, indicating that the site preference of male C. smaragdinus was largely maintained during the adult season. Three indexes of territory quality based on animal preference, occupation duration (OD), initial occupation date (IOD) and the number of contests (NOC), were highly correlated. Therefore, these preference‐based indexes are consistent and reliable, although they are indirect estimates of benefits obtained from territories. Males arriving at territory sites early in the season were more likely to hold territories of better quality when NOC was used as the index of territory quality. The positive relationship between territory quality and male arrival date is congruent with the result of a previous study showing that early comers tend to hold a territory whereas late comers do not. However, male arrival date was not related to territory quality when OD or IOD was used as an index of territory quality. One possible reason for this apparent discrepancy is that the coefficient of variation of NOC is larger than those of OD and IOD, and therefore NOC could evaluate territory quality more quantitatively than the other two indexes. To date, studies of territoriality in butterflies have not considered the quality of territories. More studies considering the quality of territories will provide new insights into butterfly territoriality.