Scott L. Kight

Evidence of population-level lateralized behaviour in giant water bugs, Belostoma flumineum Say (Heteroptera: Belostomatidae) : T-maze turning is left biased

Lateralized behaviour occurs in diverse animals, but relatively few studies examine the phenomenon in invertebrates. Here we report a population-level left turn bias in the giant water bug Belostoma flumineum Say (Heteroptera: Belostomatidae) in an underwater T-maze. Individuals made significantly more left turns than right turns, including when they were naïve and first introduced to the maze. Water bugs also showed significantly longer runs of consecutive left turns than right turns (i.e. LLLLL). The length of these runs, however, did not increase with experience in the maze, suggesting that the effect is not the result of learning. There were also no differences in turning bias between male and female water bugs. The proximate mechanism(s) underlying the left turn bias is unknown, but directional cues in the environment were eliminated by rotating the maze 180 degrees between experiments, suggesting the mechanism(s) is endogenous. To our knowledge this is the first study of lateralized behaviour in the Heteroptera or in a swimming invertebrate animal.

Factors affecting the allocation of paternal care in waterbugs (Belostoma flumineum Say)

SummaryMale giant waterbugs (Belostoma flumineum Say) brood eggs oviposited on their dorsa by conspecific females. Laboratory observations indicate that viable egg pads are occasionally discarded before hatching. Theory predicts that such behavior should occur only if the costs incurred by brooding exceed the benefits of hatching the egg pad. We studied the effects of egg pad size, time invested in brooding, and egg viability upon the continuation of paternal care in the giant waterbug. We found that smaller egg pads are less likely to hatch than larger ones, and males appear to be less likely to discard egg pads as temporal investment increases. However, the inviability of eggs did not appear to affect the probability of an egg pad being discarded. Males of this species appear to have evolved a decision-making process involving the continuation of paternal care.

Reproductive ecology of terrestrial isopods (Crustacea: Oniscidea)

Terrestrial isopods (Crustacea: Oniscidea) are important detritivores in many ecosystems. Because reproductive success and population dynamics of the Oniscidea depend on diverse biotic and abiotic environmental factors, the effects of global climate change on their biology may be significant. Although few studies have examined the relationship between climate change and population ecology in terrestrial isopods, much is known about their environment, genetics, physiology, behavior, life history, population biology, and evolutionary patterns. This review addresses the influence of biotic and abiotic environmental factors on terrestrial isopod reproduction. Significant biotic factors include microorganism-mediated sex determination, mate choice, sperm competition, maternal effects, food availability, and predation. Significant abiotic factors include temperature and moisture regimes, photoperiod, altitude, latitude, and microhabitat diversity. Studies of these factors reveal general patterns, as well as informative exceptions, in the ways different oniscid species, as well as different populations within a species, respond to environmental variation.

Response of terrestrial isopods, Armadillidium vulgare and Porcellio laevis (Isopoda: Oniscidea) to the ant Tetramorium caespitum: morphology, behavior and reproductive success

Summary Little is known about the effects of predatory stress on reproduction in terrestrial isopods (Crustacea: Oniscidea). We studied direct and indirect influences of predatory ants Tetramorium caespitum (Hymenoptera: Formicidae) on the behavior and reproduction of two terrestrial isopods, Armadillidium vulgare and Porcellio laevis. A. vulgare females were more cryptic than P. laevis females in both the presence and absence of ants, but in both species control animals were more cryptic than experimental animals exposed to ants. This likely resulted from increased movement in the presence of ants. Both species also avoided ventilated enclosures containing ants, but control animals not previously exposed to ants remained significantly further away. P. laevis also remained significantly further from ants than A. vulgare, suggesting that P. laevis more actively avoids potential predators. This is consistent with morphological differences between the two species: A. vulgare can roll into a sealed ball whereas the morphology of P. laevis permits swift locomotion. Furthermore, mortality rates of P. laevis were greater than A. vulgare when both were directly exposed to ants in the laboratory, and P. laevis suffered significantly more attacks than A. vulgare under experimental conditions. However, the length of the brooding period in A. vulgare was shorter in ant-exposed females than in controls, whereas experimental and control P. laevis females showed no such difference. This could be an adaptive trade-off for A. vulgare because in the late brooding period the distended marsupium can prevent rolling into a closed ball for protection. The results of this study underscore the relationships between morphology, behavior, and reproductive success.

TURN ALTERNATION IN RESPONSE TO SUBSTRATE VIBRATION BY TERRESTRIAL ISOPODS, PORCELLIO LAEVIS (ISOPODA: ONISCIDEA) FROM RURAL AND URBAN HABITATS IN NEW JERSEY, U.S.A

ABSTRACT Terrestrial isopods are known to increase alternating maze turns in response to adverse environmental conditions, a behavioral pattern presumably associated with efficient escape. The present study investigates whether turning behavior in response to vibration disturbance differs between natural populations inhabiting disturbed and undisturbed areas. Some specimens were collected from urban habitat characterized by construction and heavy automobile traffic, and others from relatively undisturbed rural habitat less than 10 kilometers distant. We examined maze turn alternation in three groups: rural and urban terrestrial isopods exposed to vibration during testing, and rural isopods not exposed to vibration. As predicted, rural isopods exposed to vibration made significantly more turn alternations than rural isopods not exposed to vibration. However, rural vibration-exposed isopods also exhibited significantly greater turn alternation than vibration-exposed urban isopods. There was no significant difference between rural non-exposed and urban vibration-exposed isopods. These results indicate that isopods increase turn alternation when disturbed, but that previous exposure to disturbance is associated with a reduction in the effect. Whether this is due to acclimated or evolved behavioral mechanisms is presently unknown.

Termination of parental care in male giant waterbugs, Belostoma flumineum Say (Heteroptera: Belostomatidae) is associated with breeding season, egg pad size, and presence of females

Reproductive effort and/or success sometimes increase with the age of a parent. We found that reproductive effort was greatest in older egg-brooding male giant waterbugs, Belostoma flumineum Say. Consistent with previous studies, males with large egg pads were unlikely to discard them unhatched under any condition. However, males with small egg pads were significantly more likely to discard the eggs unhatched in the autumn (when breeding adults are young) than in the spring. By brooding smaller pads, older males invested more heavily in each offspring. Males bearing small egg pads were also significantly less likely to discard them in the presence of females. Three kinds of hypotheses have previously been proposed to explain why reproductive investment and/or success might increase with age: selection hypotheses predict differential survival of better parents; experience hypotheses predict that more experienced parents achieve greater success without additional cost per offspring; and residual reproduction hypotheses predict that older parents invest more per offspring. It is difficult to experimentally untangle these hypotheses, but the results of this study provide cautious support for a residual reproduction hypothesis that older males with few remaining reproductive opportunities invest more heavily per offspring by retaining small egg pads.

Do Predator Cues Influence Turn Alternation Behavior in Terrestrial Isopods Porcellio laevis Latreille and Armadillidium vulgare Latreille

Terrestrial isopods (Crustacea: Oniscidea) make more alternating maze turns in response to negative stimuli, a navigational behavior that corrects divergence from a straight line. The present study investigates this behavioral pattern in two species, Porcellio laevis Latreille and Armadillidium vulgare Latreille, in response to short-term vs. long-term exposure to indirect cues from predatory ants. Neither isopod species increased the number of alternating turns in response to short-term indirect exposure to ants, but both species made significantly more alternating turns following continuous indirect exposure to ants for a period of one-week. These results are surprising given differences in behavioral and morphological predator defenses between these species (the Armadillidiidae curl into defensive postures when attacked, whereas the Porcellionidae flee). The marked similarity in alternating turn behavior of the two families suggests evolutionary conservation of antipredator navigation mechanisms.