Sexual Cannibalism in the Brown Widow Spider (Latrodectus geometricus)

Sexual cannibalism may represent an extreme form of male monogamy. According to this view, males gain reproductive success by sacrificing themselves to females. We studied the occurrence and timing of sexual cannibalism in the brown widow spider Latrodectus geometricus and compared male courtship and mating behavior with virgin and with previously mated females. We found that events of sexual cannibalism are frequent, that they occur during copulation and that males initiate cannibalism by placing the abdomen in front of the female’s mouth‐parts during copulation (somersault behavior). Both the somersaults and mating occurred more frequently with virgins than with previously mated females. Our results support the hypothesis that sexual cannibalism is a male strategy in this species. The somersault behavior was previously known only from the redback spider, Latrodectus hasselti. It is as yet unknown whether self‐sacrifice has evolved more than once in this genus.     

The Effect of Limb Loss on the Courtship and Mating Behavior of the Wolf Spider Pardosa milvina (Araneae: Lycosidae)

Limb loss is common in the wolf spider Pardosa milvina, appearing in nearly one third of adult males but occurring less frequently among adult females and juveniles. Since males wave their first pair of legs during courtship displays, the reproductive consequences of limb loss may be significant. We measured the courtship and mating effects of the loss of one, two, or four legs among adult male P. milvina. Missing one or two legs did not significantly reduce a male's ability to mate, but missing four legs was detrimental to mating success, reduced both courtship intensity and copulation duration, and increased cannibalism frequency. Results suggest behavioral flexibility in compensating for limited leg loss and a defensive function of the anteriormost legs to thwart female cannibalism attempts.     

Interspecific interactions in a tri-trophic arthropod system: effects of a spider on the survival of larvae of three predatory ladybirds in relation to aphids

The effects of the crab spider, Misumenops tricuspidatus (Fabricius), on the larval survival of three ladybird species, Harmonia axyridis Pallas, Coccinella septempunctata L., and Propylea japonica L., in relation to aphids were investigated in the laboratory. Predation by the spider on the three ladybird species differed. All the larvae of C. septempunctata, none of H. axyridis, and an intermediate number of P. japonica were attacked and eaten by the spider. All the larvae of H. axyridis suffered mortality due to cannibalism or starvation in the treatments with and without a spider. In case of C. septempunctata, however, mortality in the early instars was significantly greater in the treatment with a spider than without a spider and no larvae developed into pupae due to predation. In the treatment without a spider, the majority of the larvae in the former treatment suffered mortality due to cannibalism or starvation, and only 13.3% of larvae developed into the adult stage. In the case of P. japonica, mortality was mainly attributed to predation in the treatment with a spider and only 26.7% became adult. In comparison, 86.7% of larvae survived to the adult stage in the treatment without a spider. In addition, in both H. axyridis and C. septempunctata, the development of young larvae was significantly slower in the presence of a spider, but this was not the case with the older larvae of H. axyridis, which indicates that the effect of the spider on larval development changed with the developmental stage of the larvae in this species. However, the spider had no significant effect on the developmental time of P. japonica larvae. Although both the spider and the ladybirds significantly affected the number of aphids, they did not have an additive effect on aphid abundance. The interactions between the spider and the ladybirds, such as intraguild predation or competition, caused them to reduce aphid population density less than the ladybirds did on their own. The effect of the spider on the larval performance of three predatory ladybirds was found to be unequal in terms of their vulnerability to predation and rate of larval development and it depended on the species and developmental stage of the ladybird.     

Limits to Male Copulation Frequency: Sexual Cannibalism and Sterility in St Andrew's Cross Spiders (Araneae, Araneidae)

Sexual cannibalism is common among orb‐web spiders and may limit male copulation frequency. Each copulation by male St Andrew's Cross spiders (Argiope keyserlingi) involves the transfer of sperm from one pedipalp only. Almost half of the males survive their first copulation, but all of the surviving males are cannibalized when they copulate with the other pedipalp. We investigated why males cannot copulate more than twice. Experimentally fatigued males were not cannibalized more frequently than control males. Experimental removal of one pedipalp in virgin males did not increase cannibalism during their first copulation, but the surviving males were unable to copulate with a subsequent female, suggesting they cannot use a pedipalp more than once. Un‐manipulated males always inserted their unused pedipalp during their second copulation. Sperm counts from males preserved immediately after copulation and from males maintained for an additional 3 wk show that used pedipalps are not replenished over such a period.     

Host‐mediated induction of α‐amylases by larvae of the Mexican bean weevil Zabrotes subfasciatus (Coleoptera: Chrysomelidae: Bruchinae) is irreversible and observed from the initiation of the feeding period

Larvae of Zabrotes subfasciatus secrete α‐amylases that are insensitive to the α‐amylase inhibitor found in seeds of Phaseolus vulgaris. By analyzing amylase activities during larval development on P. vulgaris, we detected activity of the constitutive amylase and the two inducible amylase isoforms at all stages. When larvae were transferred from the non α‐amylase inhibitor containing seeds of Vigna unguiculata to P. vulgaris, the inducible α‐amylases were expressed at the same level as in control larvae fed on P. vulgaris. Interestingly, when larvae were transferred from seeds of P. vulgaris to those of V. unguiculata, inducible α‐amylases continued to be expressed at a level similar to that found in control larvae fed P. vulgaris continuously. When 10‐day‐old larvae were removed from seeds of V. unguiculata and transferred into capsules containing flour of P. vulgaris cotyledons, and thus maintained until completing 17 days (age when the larvae stopped feeding), we could detect higher activity of the inducible α‐amylases. However, when larvae of the same age were transferred from P. vulgaris into capsules containing flour of V. unguiculata, the inducible α‐amylases remained up‐regulated. These results suggest that the larvae of Z. subfasciatus have the ability to induce insensitive amylases early in their development. A short period of feeding on P. vulgaris cotyledon flour was sufficient to irreversibly induce the inducible α‐amylase isoforms. Incubations of brush border membrane vesicles with the α‐amylase inhibitor 1 from P. vulgaris suggest that the inhibitor is recognized by putative receptors found in the midgut microvillar membranes. © 2010 Wiley Periodicals, Inc.     

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.     

Pattern of sperm transfer in redback spiders: implications for sperm competition and male sacrifice

Many sperm competition studies have identified copulation durationas an important predictor of paternity. This result is ofteninterpreted as a sperm transfer effect—it is assumed thatsperm transfer is limited by copulation duration. Here we testthe assumption of duration-dependent sperm transfer in the Australianredback spider, Latrodectus hasselti, in which a correlationbetween copulation duration and paternity has been implicatedin the evolution of a rare male self-sacrifice behavior. Maleredbacks facilitate sexual cannibalism by females during copulation.Sexual cannibalism is apparently adaptive for redback males,in part because it results in longer copulations (25 versus11 min.), and copulation duration is positively correlated withpaternity. We assessed sperm transfer in normal copulationsand in copulations that we terminated at 5, 10, or 20 min. Ourresults show that the paternity advantage of sexual cannibalismis not owing to time-dependent sperm transfer, as redback malestransfer the majority of their sperm within the first 5 minof copulation. This suggests that the link between copulationduration and paternity may instead be owing to cryptic femalechoice or the transfer of nongametic ejaculatory substances.Results further indicate that the act of cannibalism itselfmight play a role in mediating sperm transfer. This study highlightsthe importance of understanding mechanisms of sperm transferwhen attempting to interpret the outcome of sperm competitionstudies.     

Effect of a non‐host plant Phaseolus vulgaris on larval performance and oviposition of the oriental tobacco budworm Helicoverpa assulta (Lepidoptera: Noctuidae)

The oriental tobacco budworm, Helicoverpa assulta, is a specialist herbivore feeding on a few plants of the Solanaceae family including tobacco. Larval performance and adult oviposition of H. assulta were investigated in a non‐host plant, Phaseolus vulgaris (Fabaceae) in comparison with two solanaceous host plants, Nicotiana tabacum and Datura stramonium. Larvae provided with the P. vulgaris leaf died off at day 15, whereas 50% and 40% of larval populations fed on the leaves of N. tabacum and D. stramonium, respectively, survived at day 15. Larval growth upon feeding showed significant difference between the non‐host plant (P. vulgaris) and the host plants (N. tabacum and D. stramonium), but it was not significantly different between the two host plants. In the no‐choice experiment of oviposition, gravid females laid more eggs in N. tabacum and D. stramonium than in P. vulgaris. When the most likely acceptable host plant, N. tabacum, and the non‐host plant, P. vulgaris, were subjected to the choice experiment of oviposition, H. assulta females preferred to lay eggs in N. tabacum, where eggs were continuously laid during the whole experiment period. However, eggs in P. vulgaris were hardly detected throughout the period. This study showed that the non‐host plant, P. vulgaris, had a negative influence on the larval performance and adult oviposition of H. assulta, implying neonate stage is critical for larval survivorship, and ovipositional preference by the female is highly specialized to host plants. Further investigation is required to identify non‐host factors, which could be applied to the development of alternative pest management strategy against H. assulta.     

A secondary sex trait under construction: age- and nutrition-related salivary gland development in a scorpionfly (Insecta: Mecoptera)

Males of Panorpa vulgaris Imhoff and Labram, 1836 (Insecta: Mecoptera) can apply three alternative mating tactics to gain access to female mating partners: (1) without nuptial feeding, (2) providing females with a dead arthropod or (3) producing salivary masses. Providing females with salivary masses during copulation leads to the highest reproductive success, as it results in longer mating durations relative to the other tactics. While the number of sperm transferred correlates with the duration of copulation, the sperm of different males are used according to the fair raffle model. Therefore, salivary mass production is an important fitness determining factor for males. In order to provide females with salivary masses, males must first produce and store saliva secretion inside their salivary glands. The present study was concerned with the development of male salivary glands (= production of saliva) in the course of time after adult emergence. We can show that saliva production did not start before adult emergence, that the state of development of salivary glands was affected by larval nutrition as well as by adult nutrition and, moreover, by age. Older individuals had developed glands of greater mass than had younger animals. After receiving a one‐time feeding immediately after eclosion salivary gland mass increased, while body mass decreased with age. Therefore, male P. vulgaris were able to enlarge the amount of their mating resources (= saliva) independently from external nutritional supply (after the initial feeding) and at the expense of losing weight. Possible reasons and functional explanations are discussed.     

Metabolic rates during rest and activity in differently tracheated spiders (Arachnida,Araneae):<Emphasis Type="Italic"> Pardosa lugubris</Emphasis> (Lycosidae) and<Emphasis Type="Italic"> Marpissa muscosa</Emphasis> (Salticidae)

With flow-through respirometry under video tracking, the CO₂ release of adult male and female Pardosa lugubris (wolf spider) and Marpissa muscosa (jumping spider) was measured during rest and activity. Activity metabolism was measured in phases in which the animals were spontaneously active and during forced exercise. Standard metabolic rates (V_CO2/t) were 1.43 nmol s^–1 g^–1 in M. muscosa and 1.7–1.8 nmol s^–1 g^–1 in P. lugubris. Egg production caused higher resting rates in females compared with the males in P. lugubris. Maximum mass-specific CO₂ release, the additional amount of CO₂ released after activity and the factorial aerobic scope were higher in M. muscosa. Additionally, half-time recovery and the lag between end of activity and maximum CO₂ release were lower in the jumping spider. The results are consistent with the hypothesis that the well-developed tracheal system in jumping spiders increases the efficiency of the respiratory system in comparison with wolf spiders, which possess similarly developed lungs but only a simple tracheal system that is restricted to the opisthosoma.Communicated by G. Heldmaier     

Remote copulation: male adaptation to female cannibalism

Sexual cannibalism by females and associated male behaviours may be driven by sexual conflict. One such male behaviour is the eunuch phenomenon in spiders, caused by total genital emasculation, which is a seemingly maladaptive behaviour. Here, we provide the first empirical testing of an adaptive hypothesis to explain this behaviour, the remote copulation, in a highly sexually cannibalistic orb-web spider Nephilengys malabarensis. We demonstrate that sperm transfer continues from the severed male organ into female genitals after the male has been detached from copula. Remote copulation increases the total amount of sperm transferred, and thus probably enhances paternity. We conclude that the mechanism may have evolved in response to sexual cannibalism and female-controlled short copulation duration.     

Cannibalism and Virus Production in Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) Larvae Fed with Two Leaf Substrates Inoculated with Baculovirus spodoptera

Cannibalism in the fall armyworm, Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) (FAW), is a limiting factor in a baculovirus production system. To detect the impact of cannibalism, a two-step bioassay was conducted with different larval ages of FAW fed on two food sources (corn and castor bean leaves) contaminated with the S. frugiperda multiple-embedded nucleopolyhedrovirus. In a first bioassay, the food source affected the cannibalism, being higher for all larval ages tested (5-, 6- and 7-day-old larvae) in larvae fed on corn than on those fed on castor bean leaves. Larval mortality, weight equivalent and larval equivalents (LEs) per hectare decreased as the larval age increased. Larval weight, occlusion bodies (OBs)/larva and total OBs increased when the larval age increased. In a second bioassay, in which only 6- and 7-day-old larvae were used because of the performance in the first bioassay, the cannibalism rates were affected by the interaction between food sources and time of feeding (48 and 72 h), reaching the highest values for 6- and 7-day-old larvae fed on corn leaves for 72 h. Mortality of the FAW was affected by the interaction between food sources, larval age and time of feeding. The lowest mortalities were on 7-day-old larvae when they were fed on castor bean leaves for 48 and 72 h. Larval weight, OBs/larva, total OBs and LEs were affected by the interaction between food sources and larval age. A significant correlation was observed between larval weight and OBs/larva that fed on both food sources, suggesting that larval weight can be used to achieve a concentration to be sprayed in 1 ha.     

Larval morphometry of the Japanese flounder,Paralichthys olivaceus

The larval development of the Japanese flounder,Paralichthys olivaceus, was surveyed using two types of morphometric analyses, modified allometry and polar coordinate analysis by principal component analysis (PCA). In the former, centroid size was used as a growth index instead of total length (TL), such enabling the determination of more detailed changes in each character than ordinary allometry based upon TL. Polar coordinate analysis disclosed two remarkable inflexions during the larval development ofP. olivaceus. Postlarvae ofP. olivaceus were found to undergo four developmental phases. From the point of view of metamorphosis, the phases were named drifting larva, premetamorphic larva, metamorphic larva and postmetamorphic larva, respectively. These phases were also tested by other characters related to flounder metamorphosis.     

Differential Kin Discrimination by Red-spotted Newts (Notophthalmus viridescens) and Smooth Newts (Triturus vulgaris)

In organisms lacking parental care or when eggs of more than one female are layed together, parents preferentially tend to avoid eating their own offspring. In some species of newts (Caudata: Salamandridae), there is no parental care and cannibalism of eggs and larvae occurs when philopatric adults remain in the pond throughout the breeding season where eggs and larvae develop. Kin discrimination by both adult newts and larvae would be expected to occur during the breeding season as it would enable individuals to benefit from the nutrients obtained from eating eggs and larvae while they avoid eating close relatives. The effects of kinship on cannibalism of eggs and larvae were examined in two species of newts. In separate, but similar, paired behavioral trials adult female red-spotted newts, Notophthalmus viridescens, and smooth newts, Triturus vulgaris, were allowed to consume their own egg or an egg from another female. Female red-spotted newts, but not smooth newts, preferred to eat eggs of other females rather than their own, and overall smooth newts were ‘reluctant’ to eat conspecific eggs. To test for ontogenetic shifts in discrimination abilities, additional experiments were performed with adult female red-spotted newts paired with their own larvae and a larva from another female. In addition, the effects of kinship on the attraction or repulsion of larvae was also studied in red-spotted newts. Females showed no significant discrimination abilities during acts of cannibalism on larvae. Larvae spent similar amounts of time with siblings and non-siblings. These results suggest that the ability of adult newts to discriminate among eggs varies between species and that the elicitation of a kin-discrimination response may be context-dependent. For red-spotted newts, there was no evidence of discrimination abilities within and between other life-history stages.     

Life history of the spider parasitoid Zatypota percontatoria (Hymenoptera: Ichneumonidae)

The life history of polysphinctine parasitoids is poorly understood. As a result, their effect on their host has not been evaluated. Here, we present the phenology of Zatypota percontatoria, an ectoparasitoid wasp of theridiid spiders, using rich field, semi‐field and laboratory investigations of selected life‐history parameters. The wasps overwintered as larva attached to the spider abdomen and the imagos of the first generation emerged at the beginning of May. The sex ratio (F/M) of overwintered wasp larvae was 1.4. The wasp spent an average of 6.4 days in the egg stage, 27.67 days in the larval stage and 9.6 days in the pupal stage. Adult longevity was on average 14.34 days. Oviposition occurred on average 8.44 days following maturity. The wasp laid on average 0.35 eggs/day. The total fecundity was on average 7.4 eggs per wasp and decreased with age (data from unmated females). The developmental rate increased with experimental temperature up to 28 °C. The lower developmental threshold for pupae was estimated at 6.6 °C. The sum of effective temperatures for pupae was estimated at 157.8 degree days. Using daily temperature records from the Czech Republic over the last 41 years, we estimated an average of 3.5 generations of Z. percontatoria per year. Mortality was 48% in semi‐field conditions and 23% in the laboratory. The incidence of mortality was highest during egg and larval stages caused by the detachment of eggs or larvae during spider molting, the mortality of the spider‐host and egg deposition on the spider prosoma.     

Laboratory studies on larval growth ofPolydora ligni,Polydora ciliata,andPygospio elegans (Polychaeta,Spionidae)

The spionid polychaete speciesPolydora ligni, P. ciliata, andPygospio elegans were cultivated in the laboratory over several successive generations. A flow-through cultivation system forPolydora spp. is described. Duration of life cycles (time from hatching of the larva to first reproduction) and life spans (hatching to death) of these species were not significantly influenced by the degree of inbreeding nor by individual age of the parents. Minimum time from metamorphosis (15-setiger stage) to first hatching of offspring larvae (in the 3-setiger stage) at 18°C was 33 days inPolydora spp. and 81 days inPygospio elegans. Larval growth patterns are described in terms of number of setigers, body length, and biomass (dry weight, carbon, nitrogen, hydrogen), in relation to time after hatching. Regression models are proposed which link these measures of larval growth and, thus, may be used for conversions. Rates of development and growth show a high degree of variability in all three species, not only caused by variation in environmental factors such as temperature or food, but also among and within single hatches of larvae reared under identical conditions. Larvae were reared at constant temperatures (6°, 12°, and 18°C). Temperature affected larval growth inPolydora ligni more than inP. ciliata, and least of all inPygospio elegans. Only the latter species was able to develop at 6°C from hatching to metamorphosis. This differential response may be explained by differences in the natural spawning season of these species. Eleven phytoplankton species were tested as to their food values. A relative index of growth is proposed which compares the slopes of two growth curves (one standard and one test condition). The flagellateDunaliella tertiolecta was used as a standard food in these experiments. Most algal species were less suitable, and only the diatomThalassiosira rotula was consistently better food for spionid larvae thanD. tertiolecta.     

Eat or Not to Eat: Reversed Sexual Cannibalism as a Male Foraging Strategy in the Spider Micaria sociabilis (Araneae: Gnaphosidae)

Reversed sexual cannibalism represents an unusual situation in which a male kills and consumes a female. We examined this rare phenomenon in the spider Micaria sociabilis, whose males were observed to regularly cannibalise old females. In this study, we investigated male motivation for such behaviour in the light of ecological conditions such as mate availability and prey availability. We found that male cannibalism is not affected by short‐term starvation but rather by male feeding history during the ontogenetic development in combination with prey availability during the adult stage. Males from the summer generation reached bigger sizes than males from the spring generation and females from both generations. They developed in the period with exceptionally high prey occurrence, but when they reached the adult stage, the prey availability decreased. In this period, we observed the highest frequency of cannibalism, however, only when the sex ratio was female biased. Reversed sexual cannibalism in M. sociabilis seems to represent an advantageous male foraging strategy, which is affected by prey availability and male feeding history, tuned by sex ratio and directed towards females of inferior quality.     

Mate discrimination in Littorina littorea (L.) and L. saxatilis (Olivi) (Mollusca:Prosobranchia)

The ability of males of Littorina littorea and L. saxatilis to discriminate between mates of different sex, species and size was examined. In partner choice experiments males of L. littorea had the possibility to initiate a copulation with either a female or a male. The males did not show a preference for either sex. There was therefore no evidence that they could determine the sex of a conspecific prior to copulation. The duration of intrasexual copulation was considerably shorter than for intersexual copulation, both in the field and in laboratory experiments. For the two species, intersexual copulations were far more frequent than intrasexual ones. This can partly be explained by the difference in copulation time.Few interspecific copulating pairs were found on the shore. This may reflect a low interspecific encounter rate rather than a mechanism of species recognition. On all of these occasions, however, the active male was of L. saxatilis. It is argued that selection against precopulatory species and sex recognition is a more likely explanation than an hypothesis that states that the required mutations for precopulatory mate identification has not yet occurred. L. littorea males copulated longer with large than with small females. Copulation time was short with parasitized females, which are sterile or of low fecundity. The allocation of mating effort by males is discussed.     

Sperm storage and copulation duration in a sexually cannibalistic spider

Female St Andrew’s Cross spiders control copulation duration by timing sexual cannibalism and may thereby control paternity if cannibalism affects sperm transfer. We have investigated the effect of copulation duration on sperm transfer and documented sperm storage patterns when we experimentally reduced the ability of females to attack and cannibalise the male. Virgin males and females were paired and randomly allocated either to a control treatment, where females were allowed to attack and cannibalise the male during copulation, or to an experimental treatment, where females were unable to cannibalise the male. The latter was achieved by placing a paintbrush against her chelicerae during copulation. Our experimental manipulation did not affect copulation duration or sperm storage. However, the number of sperm stored by the female increased with copulation duration only if the male was cannibalised, suggesting that cannibalism increases relative paternity not only through prolonged copulation duration following a fair raffle model but also through the cannibalism act itself. Future studies should explore whether cannibalised males ejaculate more sperm or whether females selectively store the sperm of cannibalised males.     

Genetic and phenotypic variation for flight ability in the cactophilicDrosophila species,D. aldrichi andD. buzzatii

The flight ability ofDrosophila aldrichi (Patterson & Crow) andD. buzzatii (Patterson & Wheeler) using tethered flights, was measured with respect to age-related changes, genetic variation and adult body size variation induced by rearing at different larval densities.Drosophila buzzatii flew for much longer thanD. aldrichi, especially females, but age-related changes in flight duration were significant only forD. aldrichi. Effects of body size on flight ability were significant inD. buzzatii, but not inD. aldrichi. InD. buzzatii, there was a significant genotype-environment interaction (larval density × line) for flight duration, with short and average flight duration isofemale lines showing longer flights, but a long flight duration line shorter flights as body size decreased (i.e., as larval density increased). Heritability estimates for flight duration were similar in the two species, but flight duration showed no significant genetic correlations with developmental time, body size or wing dimensions (except for one wing dimension inD. buzzatii). Although not significantly different between the species, heritabilities for life-history traits (adult size and developmental time) showed contrasting patterns — with higher heritability for body size (body weight and thorax length) inD. buzzatii, and higher for developmental time inD. aldrichi. In agreement with limited previous field evidence,D. buzzatii is better adapted for colonization than isD. aldrichi.