Flight movement of Scapanes australis australis (Boisduval) (Coleoptera: Scarabaeidae: Dynastinae) in Papua New Guinea: a radiotelemetry study

Abstract We used radiotelemetry and/or chemical light-tags to track the flight of 15 individuals of Scapanes australis in Madang Province, Papua New Guinea. This species causes severe economic impacts on coconut palms in young plantations. Flights to feeding, mating, resting, and possibly oviposition sites covered distances of 52 to 835 m in males, and from 245 m to>1000 m in females. Upon release, females flew in a tight upward spiral above canopy level (>20 m), then usually flew along a single bearing out of radio reception within 1 min of initiating flight. Dispersing females probably follow scent trails to pheromone-releasing males that occupy feeding galleries excavated most frequently in coconut palms, or search for oviposition sites. Most tagged females were not found again, because they dispersed beyond the tracking capabilities of our radio-receivers, but one female was followed for 245 m to a feeding gallery excavated by an adult male. Males typically flew within 5 m of the ground, took erratic flight paths with numerous turns, and frequently circled coconuts and other host plants. We followed males from the release point until they ceased flight for a night. Males passed daylight hours either in a feeding gallery within a host plant or under soil litter.     

Proximate determination of male horn dimorphism in the beetle Onthophagus taurus (Coleoptera: Scarabaeidae)

The existence of discrete phenotypic variation within one sex poses interesting questions regarding how such intrasexual polymorphisms are produced and modified during the course of evolution. Approaching these kinds of questions requires insights into the genetic architecture underlying a polymorphism and an understanding of the proximate mechanisms determining phenotype expression. Here we explore the genetic underpinnings and proximate factors influencing the expression of beetle horns – a dramatic sexually selected trait exhibiting intramale dimorphism in many species. Two relatively discrete male morphs are present in natural populations of the dung beetle Onthophagus taurus (Scarabaeidae, Onthophagini). Males exceeding a critical body size develop a pair of long, curved horns on their heads, while those smaller than this critical body size remain essentially hornless. We present results from laboratory breeding experiments designed to assess the relative importance of inherited and environmental factors as determinants of male morphology. Using father–son regressions, our findings demonstrate that horn length and body size of male progeny are not predicted from paternal morphology. Instead, natural variation in an environmental factor, the amount of food available to larvae, determined both the body sizes exhibited by males as adults and the presence or absence of horns. The nonlinear scaling relationship between the body size and horn length of males bred in the laboratory did not differ from the pattern of variation present in natural populations, suggesting that nutritional conditions account for variation in male morphology in natural populations as well. We discuss our results by extending ideas proposed to explain the evolution of conditional expression of alternative phenotypes in physically heterogeneous environments toward incorporating facultative expression of secondary sexual traits. We use this synthesis to begin characterizing the potential origin and subsequent evolution of facultative horn expression in onthophagine beetles.     

Male differentiation patterns in two polyphenic sister species of the genus Onthophagus Latreille, 1802 (Coleoptera: Scarabaeidae): a geometric morphometric approach

This paper focuses on morphological (both shape and size ) differences that quite similar polyphenic sister species evolve during divergence processes. Traits were analysed using a geometrical morphometric approach, which has the ability to evidence also very subtle differences in shape. As a case study, we considered males of the dung beetle sister species pair Onthophagus taurus and Onthophagus illyricus (Coleoptera, Scarabaeidae); these species represent a typical example of polyphenic trait expression concerning the facultative development of horns and considerable body size differences. External shape morphology failed to discriminate O. taurus from O. illyricus , whereas the reproductive system shape showed significant interspecific discrimination power. However, the head of O. taurus was significantly larger than that of O. illyricus and the reverse was true for the elytra. The two species also showed different allometric values of the head with respect to body size. This complex pattern of interspecific morphological divergence is discussed in the light of the differential trait divergence rate hypothesis. In both species, differences between major and minor forms concern the overall shape of head and pronotum: we suggest that such different forms, which likely reflect morphological readjustment to accommodate horns of considerable bulk and disproportionate length, may be nevertheless advantageously used by the two male morphs in their alternative reproductive tactics. Male genitalia sizes were virtually constant with respect to body size; however, the ratio between phallotheca and body size was significantly higher in minor males, in keeping with the hypothesis of a higher investment in genitalia borne by this morph.     

Sexual and male horn dimorphism in Copris ochus (Coleoptera: Scarabaeidae)

Copris ochus (Coleoptera: Scarabaeidae), an endangered species, is the largest dung beetle in Japan. In C. ochus, males have a long head horn, while females lack this long horn (sexual dimorphism). Very large males of C. ochus have disproportionately longer head horns than small males, suggesting male horn dimorphism, although the dimorphism has not been investigated quantitatively. To clarify sexual and male horn dimorphism in C. ochus quantitatively, we examined the scaling relationship between body size (prothorax width) and head horn length in 94 females and 76 males. These beetles were captured during July 1978 from a natural population on Mt. Aso in southwestern Japan using a light trap. Although the horn length of the females and males scaled with prothorax width, the scaling relationship differed between the sexes, i.e., the relationship was linear in females and nonlinear in males. Statistical tests for dimorphism in male horn length showed a significant discontinuous relationship, thus indicating distinct sexual and male dimorphism in head horns. Long- and short-horned C. ochus males may have different reproductive behaviors, as described in other horned dung beetles.     

Horn polyphenism and related head shape variation in a single-horned dung beetle: Onthophagus (Palaeonthophagus) fracticornis (Coleoptera: Scarabaeidae)

Horns of Onthophagus beetles are typical examples of phenotypically plastic traits: they are expressed as a function of environmental (nutritional) stimuli, and their reaction norm (i.e. the full set of horn lengths expressed as a response to different degrees of nutritional states) can be either linear or threshold-dependent. Horned males of Onthophagus ( Palaeonthophagus ) fracticornis (Preyssler, 1790) bear a single triangular cephalic protrusion of vertex carina, which has received phylogenetic support as the most primitive horn shape in the genus. Inter- and intra-sexual patterns of horn expression were studied in O. fracticornis by means of static allometries while associated variations in head shape were assessed using geometric morphometric techniques. The relation between log-transformed measurements of body size and vertex carina supported an isometric scaling in females. On the contrary, a sigmoidal model described better the horn length-body size allometry in males, with a switch point between alternative morphs at a pronotum width of 3.88 mm. Sigmoidal static allometries of horns in Onthophagus populations arise from a threshold-dependent developmental process of horn growth. This process underlies the expression of both plesiomorphic and apomorphic horn shapes in the genus. Given that the single-horn model has been identified as primitive, we propose that such a developmental process giving rise to it may be evolutionarily ancient as well. Horn expression was accompanied by a deformation of the head which makes minor and major morphs appear even more different. Therefore, in this species both horn and head shape expression contribute to male dimorphism.     

Cyclocephala (Coleoptera: Scarabaeidae: Dynastinae) evolution in Lesser West Indies indicates a Northward colonization by C. tridentata

A dual cytogenetic and molecular analysis was performed in four species of Cyclocepala (Coleoptera: Scarabaeidae: Dynastinae) from Lesser Antilles (Martinique, Dominica and Guadeloupe). Two species/sub-species, C. mafaffa grandis and C. insulicola, are endemic to Guadeloupe. They have their own non-polymorphic karyotype and a fairly homogeneous haplotype of the COI gene. C. melanocephala rubiginosa has a distinct karyotype. Its COI haplotype is homogeneous in Guadeloupe and heterogeneous in Martinique. Finally, C. tridentata has highly different karyotypes and haplotypes in the three islands. In Martinique, its karyotype, composed of metacentrics, is monomorphic while its haplotype is fairly heterogeneous. Both are close to those of other Cyclocephala and Dynastinae species, thus fairly ancestral. In Guadeloupe, its karyotype is highly polymorphic, with many acrocentrics, and its haplotype fairly homogeneous. Both are highly derived. In Dominica, both the karyotype and the haplotype represent intermediate stages between those of Martinique and Guadeloupe. We conclude that several independent colonization episodes have occurred, which excludes that C. insulicola is a vicariant form of C. tridentata in Guadeloupe. Both chromosome and COI gene polymorphisms clearly indicate a recent colonization with a northward direction for C. tridentata.     

The influence of horn and body size on the reproductive behavior of the horned rainbow scarab beetlePhanaeus difformis (Coleoptera: scarabaeidae)

The reproductive behavior of horned rainbow scarab beetles,Phanaeus difformis, was studied to determine the influence of morphological traits on intersexual and intrasexual interactions.Phanaeus difformis is a sexually dimorphic dung beetle in which males possess much larger horns than females, and males can be grouped into major and minor male morph categories based on horn size. Male-female pairs cooperated in nest construction and provisioning. In the laboratory, males of both morphs assisted females and were equally successful at copulating. However, in the field larger individuals had a pairing advantage due to greater success in intrasexual competition. Some males used an alternative mating tactic which involved sneaking copulations with paired females. In most cases the sneak male was smaller than the paired male.     

Extreme Eye Projection in the Male Weevil <Emphasis Type="Italic">Exechesops leucopis</Emphasis> (Coleoptera: Anthribidae): Its Effect on Intrasexual Behavioral Interferences

Fungus weevils, Exechesops leucopis (Anthribidae), are sexually dimorphic in the degree of eye protrusion and antenna elongation. I examined the allometric relationships of eye span, eyestalk length, antenna length, elytra width, and wing length against body size (pronotum width), and their effects on the outcome of male-male combat in the laboratory. Male eye span, eyestalk length, and antenna length indicated positive allometry, while elytra width showed isometry, and wing length showed negative allometry. In male-male combat, males with a larger eye span, antenna length, and body size defeated those with smaller attributes. However, when males fought experimentally males of similar body size, only eye span affected the outcome of combat, independent of body size and antenna length. In the female-female contests, the prior residency was an important determinant of victory the other than any morphological traits.     

Experience-dependent recapture rates and reproductive success in male grey mouse lemurs (Microcebus murinus)

Male mating tactics can vary according to the potential for scramble or contest competition but also as a consequence of individual characteristics, such as body condition and previous experience. The influence of experience, i.e., residency, on male recapture rates and reproductive success was studied in a population of free-living grey mouse lemurs. Long-term capture data from 320 individuals revealed that both sexes had very low recapture probabilities within their first year in the study population, but recapture rates declined less sharply during the following years. Capture results and telemetric analyses on 12 focal males revealed that resident males had larger body mass and larger home ranges than new males. Home range size correlated with the number of accessible females, indicating that resident males had higher probabilities to meet mates than new males. The reproductive success of 132 candidate fathers, representing both resident and new males, was determined by means of molecular genotyping. Paternity determination was successful in 38 cases (success rate: 19%). Sixteen resident males and seventeen new males sired offspring. However, in relation to the number of candidate fathers being present in the mating season, resident males were twice as likely to reproduce successfully as new males. These findings suggest experience-dependent reproductive tactics that most likely correspond to a differential spatial knowledge of resources, mates and potential threats. The results generally agree with the predictions made for a scramble competition regime and demonstrate substantial behavioral plasticity in a nocturnal primate species with a dispersed multi-male/multi-female mating system.     

Diet alters male horn allometry in the beetle Onthophagus acuminatus (Coleoptera: Scarabaeidae)

Darwin considered the horns of male beetles to be among the most striking examples of sexual selection. As with antlers in deer or elk, beetle horns scale positively with male body size, with the result that large males have disproportionately longer horns than small males. It is generally assumed that such scaling relationships (''static allometries'') are insensitive to short-term changes in the environment, and for this reason they are regularly used as diagnostic attributes of populations or species. Here I report breeding experiments on horned beetles that demonstrate that the scaling relationship between male horn length and body size changes when larval nutrition changes. Males reared on a low-quality diet had longer horn lengths at any given body size than sibling males reared on a high-quality diet. Such ''allometry plasticity'' may explain seasonal changes observed in this same scaling relationship in a natural population. These experiments demonstrate that scaling relationships of sexually selected traits can respond facultatively to variation in the environment, thereby revealing a new mechanism by which males regulate the production of exaggerated secondary sexual traits.     

Aroid scarabs in the genus Peltonotus Burmeister (Coleoptera,Scarabaeidae, Dynastinae): key to species and new distributional data

The southeast Asian scarab beetle genus Peltonotus Burmeister (Scarabaeidae, Dynastinae, Cyclocephalini) is reviewed. New country records for Peltonotus morio Burmeister (Myanmar and Vietnam), Peltonotus nasutus Arrow (southern China and Cambodia), and Peltonotus favonius Jameson and Wada (Myanmar) are reported, including a new record in the Palearctic/Sino-Japanese biogeographic region. The first female specimen of Peltonotus favonius is described. Biological associations with aroid inflorescences are reviewed, and human consumption of Peltonotus beetles is reported. A key to all species, paralectotype designations for Peltonotus nasutus, diagnoses, and distributions using dynamic mapping tools are included.     

High chromosomal polymorphism and heterozygosity in Cyclocephala tridentata from Guadeloupe: chromosome comparison with some other species of Dynastinae (Coleoptera: Scarabaeidae)

Very distinct karyotypes have been observed in two Cyclocephala species from Guadeloupe, considered as very close and possibly vicariant: C. insulicola with only metacentric and C. tridentata tridentata with many acrocentric autosomes. This prompted us to study the karyotype of a few other neotropical Dynastinae belonging to four of the eight existing tribes, to find out which one of these two species had the most divergent chromosomes from their ancestral condition. In the four additional species studied, i.e., Cyclocephalamaffafa, Strategus syphax, Ligyrus cuniculus and Megasoma actaeon, a karyotype composed of 20 chromosomes, including 18 meta- or submetacentric autosomes was found, as it was in C. insulicola. Thus, the karyotype of C. t. tridentata, in which most of the 18 autosomes were acrocentric, is apomorphic. In addition, it was highly polymorphic, with six different karyotypes observed among the ten specimens studied. All had one to four heterozygous chromosome pairs formed by one acrocentric and one submetacentric carrying a large juxta-centromeric heterochromatic component. This heterozygosity did not seem to impair either meiotic synapsis or chiasma formation and chromosome segregation. Such high rates of chromosome heterozygosity and polymorphism are infrequent and never described in beetles. This suggests that C. t. tridentata undergoes an active process of chromosome evolution. A possible relationship with insularity and/or pesticide exposure is briefly discussed.     

The male reproductive system of Costelytra zealandica (White)(Coleoptera: Scarabaeidae: Melolonthinae)

Abstract

The morphology and histology of the male internal reproductive organs of Costelytra zealandica show many similarities to other Scarabaeoidae, and are particularly close to other Melolonthinae and to Rutelinae. Testes follicles of C. zealandica have the usual structure for Melolonthinae with basal lobes surrounding the ends of the vasa efferentia. Epithelial cells of the vasa efferentia, vasa deferentia, and vesiculae seminales have similar densely basophilic cytoplasm but muscle layers are best developed around the latter. Accessory glands lack muscle and are not differentiated histologically into regions but do differ from their reservoirs. The ejaculatory duct has a cuticular intima and is differentiated into anterior and posterior regions. Both are surrounded by a muscular sheath which expands in the posterior region to enclose fluid. This forms a hydraulic mechanism for everting the internal sac during intromission. The parameres hook into the female’s genital chamber during copulation and have no pincer action. Probable homologies are listed between muscles of the external genitalia and anus of C. zealandica and other Scarabaeoidea.     

Horn Length Is the Determining Factor in the Outcomes of Escalated Fights Among Male Japanese Horned Beetles, <Emphasis Type=Italic>Allomyrina dichotoma</Emphasis> L. (Coleoptera: Scarabaeidae)

Male horn length in some horned beetles shows a sigmoidal relationship with body size. This has often been considered as the reflection of alternative reproductive tactics of males based on body size. Large males should possess long horns to acquire females through fights with other males using their horns, whereas small males do not require long horns because they usually avoid intermale fights and adopt alternative tactics such as sneaking. This may lead to a prediction that horn length is a reliable indicator of the fighting ability of the male. We examined the effects of both male horn length and body size of Allomyrina dichotoma on the outcomes of escalated fights. Results indicate that male horn length was more important than body size in predicting the outcomes of fight, and this may support the hypothesis that the evolution of the horn dimorphism in male horned beetles is the result of different reproductive tactics.     

An Iridovirus from the black beetle,Heteronychus arator (Coleoptera : Scarabaeidae)

Abstract

Iridescent virus type 23 from the black beetle (Heteronychus arator) replicated in Spodoptera frugiperda cells, producing some cell vacuolation after 3 days and extensive vacuolation and detachment of cells 7 days after infection. The virus also replicated in Aedes albopictus cells, and in the larvae and pupae of Galleria mellonella.     

Electroantennogram responses of male Costelytra zealandica (Coleoptera: Scarabaeidae) to phenol and related compounds

Electroantennograms recorded from male New Zealand grass grub beetles, Costelytra zealandica (White), were used to compare the activity of phenol with that of closely related phenolics. These compounds had no masking effect on the antennal response. A comparison of activity between phenol and a crude female extract indicated that phenol is the sole pheromone.     

Determinants of Mating Frequency in the Spiny Orbweaving Spider,Micrathena gracilis (Araneae: Araneidae)

Male Micrathena gracilis require two copulations, separated by a dismount, in order to inseminate both reproductive tracts of the female. We examined several factors that might influence a male's copulatory success. Web structure influenced male courtship and dismount tactics, but not copulatory frequency. The presence of another male reduced the likelihood of a given male copulating with both tracts, a limitation mediated by sexual responsiveness of the female. Mating status of the female did influence copulatory frequency; males were less likely to copulate a second time with nonvirgin females. In summary, males modify mating activities to reduce predation by females, to reduce intermale competition, and to avoid expending gametes when there is little chance of fertilization. Females influence males by predatory activities, mediated through web structure, and enhancing sperm competition among males.     

The effects of resource availability on alternative mating tactics in guppies (Poecilia reticulata)

Food availability can influence the optimal allocation of timeand energy among alternative behaviors such as foraging, courting,and competing for mates. If populations differ consistentlyin food availability, selection may cause geographic divergencein allocation strategies. At the opposite extreme, a norm ofreaction may evolve such that food intake influences the allocationstrategy of individuals in the same way in all populations.Between these two extremes, food intake reaction norms may divergegenetically among populations. For example, at sites where foodis scarce, selection may strengthen the effect of food intakeon behavior, whereas at sites with abundant food, selectionmay be weak or even oppose plasticity. We tested these ideasby raising male guppies from streams differing in food availabilityin a common laboratory environment on either low or high foodlevels, and then observing them in the presence of male competitors(from the same population and diet group) and receptive females.Males from low-food-availability streams spent more time foragingthan males from high-food-availability streams, independentof food intake. Compared with males raised on the high foodlevel, males raised on the low food level spent more time foragingand were less aggressive towards other males. Courtship displayrate increased with food intake but only in males from low-foodstreams. In contrast, males from high-food streams showed greaterplasticity with respect to male-male aggression. These resultsgenerally support the resource availability/behavioral tradeoffhypothesis while also revealing a surprising degree of ontogeneticcomplexity in a relatively simple system.