Fine-scale substrate use by a small sit-and-wait predator

Substrate choice is one of the most important decisions thatsit-and-wait predators must make. Not only may it dictate theprey available but also the cover for the predator which mayconceal it from prey or its own predators. However, while ona particular substrate the behavior and use of that substratemay vary widely. When naïve, newly emerged crab spiderlingsMisumena vatia (Thomisidae) occupied flowering goldenrod Solidagocanadensis, their behavior differed markedly on inflorescenceswith relatively sparse and densely packed flower heads as wellas on experimentally thinned and unthinned inflorescences. Initially,the spiderlings most often hunted at the thinned sites and hidamong the dense flower heads at the unthinned sites, a differencethat disappeared in all broods tested after 2–3 h, possiblybecause of the growing hunger of the initially concealed individuals.Prey capture (dance flies) in the thinned sites initially significantlyexceeded that in unthinned sites but subsequently did not differ.However, spiderlings encountered their principal predator, thejumping spider Pelegrina insignis, significantly more oftenon unthinned than thinned inflorescences. Even though usagepatterns initially differed strikingly, spiderlings did notdiffer in their rates of quitting the two types of sites. Theseresults suggest a trade-off between foraging and predator avoidancethat changes in response to increasing hunger over time.     

Pick-up lines: cues used by male crab spiders to find reproductive females

The low population density of the crab spider Misumena vatiaand the high percentage of gravid adult females begs the question,how do adult males find reproductive females? We explored oneof the potential mate-locating tactics of adult males, theirline-following behavior. M. vatia do not build webs; however,they do lay down silken lines during their movements. In boththe field and the laboratory, adult males (but not juvenilemales) regularly followed lines of other individuals, as wellas their own, sometimes multiple times. However, they did notdistinguish the direction in which lines were laid, and theyeven followed lines of other species. Males responded mechanicallyto these lines, but not chemically. They followed lines ofpenultimate and adult virgin females, as well as new and old lines, with similar high frequency. Neither washing the lineswith water nor washing them with acetone (to remove possiblewater-soluble or organically soluble pheromones) affected theirchoice of lines. Due to the low activity of females, theirlines may be several days old, over which time any possible chemical information would likely dissipate. Therefore, pheromonesseem unlikely to aid males searching for unmated adult females.Nevertheless, even searching males that follow lines largelyindiscriminately should derive a benefit because concentrationsof lines could denote the presence of females and thereby maximizenumbers of females encountered.     

Choosing hunting sites with little information: patch-choice responses of crab spiders to distant cues

Adult female crab spiders (Misumena valid) released in a meadowmoved to milkweed stems more often than to other sites and alsomoved to flowering milkweed stems more often than to equallyavailable nonflowering ones. Preferences of the spiders as apopulation were similar during initial and second trials, butgiven individuals did not repeat their initial choices moreoften than predicted by chance. Thus, spiders probably respondeddirectly to cues present, rather than to information retainedfrom earlier experience. Spiders placed at the base of floweringmilkweed stems did not choose these sites more often than predictedby chance or more often than did spiders released in the grass,suggesting that this increase in localization provided no additionalinformation for choosing a hunting site. However, spiders placedat the bases of nonflowering stems selected them less oftenthan predicted. Second trials with these spiders also resembledinitial trials, but, as with the spiders released in the grass,given individuals did not repeat their initial performance moreoften than predicted. Thus, spiders released in the grass probablyresponded directly to cues present, as did spiders releasedat the base of stems. The choices of these spiders, combinedwith flexible giving-up times, caused the spiders to be concentratedon flowering stems. Although this strategy results in a better-than-randompattern of selecting hunting sites, the spiders lose considerableforaging time in the process.     

Cannibalistic behavior in red king crabs reared under artificial conditions

The cannibalistic behavior during all life history stages of the red king crab Paralithodes camtschaticus (Tilesius, 1815) raised under laboratory conditions was studied. All feeding stages were found to be cannibalistic. The major factors affecting the level of cannibalism were identified, and methods were proposed to reduce cannibalism intensity under laboratory conditions.     

贵州微蟹蛛属一新种及裸微蟹蛛的雄性新发现(蜘蛛目:蟹蛛科)

记述了产自中国贵州的微蟹蛛属Lysiteles一新种:梵净微蟹蛛L.fanjingensis sp. nov.及首次记述了裸微蟹蛛L.nudus Yu&Zhang, 2017的雄性。提供了它们的外形及外生殖器显微照片和点线覆墨图。标本保存于铜仁学院标本馆。     

Reconciling aggression and social manipulation as means of competition. 1. Life-History perspective

I reexamined male competitive options via long-term data on adolescent and adult male consort success and data on male weights, age, size, residency status, and friendships with females collected from one troop of wild baboons. The options available to a male result from a complex interaction of variables and change with maturation, migration, and age. The acquisition of aggressive and social competence, the development of alternative nonaggressive strategies, the loss of physical prowess, and perhaps the effect of inbreeding avoidance all play a role. Aggressive and nonaggressive strategies may be mutually exclusive options for brief periods in a male’s life because of ontogenetic, historical, or physical constraints. But for most of the time, the two are likely to coexist. I assess the evolutionary significance of optional strategies of competition and discuss the conditions that might select for optional strategies.     

Pure numbers,invariants and symmetry in the evolution of life histories

Summary Certain dimensionless numbers related to life histories are approximately conserved within some taxa; this suggests that the underlying life-history tradeoffs satisfy yet-to-be-discovered symmetry principles. Some possible examples are discussed.     

Mate choice by males of the hermit crab Pagurus filholi: Do males assess ripeness and/or fecundity of females?

Males of the hermit crab, Pagurusfilholi, often grasp the edges of shells occupied by females and drag them during the mating season. This behavior was experimentally confirmed to be a precopulatory guarding behavior displayed by males for ripe females, and males were found to recognize females which were within about 5 days of spawning. Most theoretical models for mating preference assume the choosing sex (the male in the present case) has complete reproductive information about potential mates, and predict that males will preferably choose more fecund females and/or females that will require less guarding time (i.e. that will spawn sooner) as partners. Several male-choice experiments between two ripe females, both previously guarded by other males, were carried out to examine the above predictions. Males did not prefer females of larger size, higher fecundity or with less time remaining until spawning. These results suggest that males may not have complete information about potential partners, rather that male hermit crabs may adopt a mating strategy of pairing with the first ripe female they encounter. Even with such incomplete mate assessment, males may enhance their reproductive success by recognizing ripe females that will spawn within a given time (about 5 days in the present case).     

Cohabitation of juvenile females with mature males promotes sexual cannibalism in fishing spiders

Precopulatory sexual cannibalism, or female predation of a potentialmate before mating, illustrates an extreme intersexual conflict.Unlike sexual cannibalism occurring after mating, precopulatorysexual cannibalism cannot be construed as a male strategy. Thus,research on the adaptive significance of this phenomenon hasfocused on female benefits. In the present study, I test theidea that precopulatory sexual cannibalism represents an adaptivefemale trade-off between the material costs and benefits ofmating with a male (forgoing food, securing sperm) and preyingon a male (forgoing sperm, securing food). I pay particularattention to the rarely tested prediction that precopulatorysexual cannibalism by virgin females should increase as eachfemale's expectation of future mating opportunities increases.I use the phenomenon of cohabitation between adult males andjuvenile females nearing sexual maturity as a means to manipulatefemale expectation of future mate availability. Results indicatethat feeding on a male has significant positive effects on severalmeasures of female fecundity. However, the likelihood of precopulatoryattacks was not explained by a female's recent feeding history.Finally, as predicted, juvenile female cohabitation with maturemales (expectation of future mating opportunities) heightensthe prevalence of precopulatory attacks by virgin females, suggestingthat juvenile experience can alter a female's propensity forsexual cannibalism. This is the first study to suggest thatjuvenile experience can alter a female's propensity for sexualcannibalism. This finding emphasizes the point that studiesof sexual selection and mating systems need to consider theeffects of juvenile experience on adult behavior.     

Life history responses depend on timing of cannibalism in a damselfly

1. Cannibalism has often been suggested as an important mechanism to reach the necessary developmental stage and size before a critical time horizon is reached, but this role has been largely unexplored. We studied effects of cannibalism on the life history of the damselfly Lestes viridis under combinations of a time constraint (by manipulating the perceived time available in the growth season) and a biotic constraint (density). 2. Larvae had a faster development and growth rate when reared at high time stress (late photoperiod). They also had a higher growth rate and mass at emergence when cannibalism occurred (density 2 and 4). Cannibalism occurred earlier at higher density. Accelerated life history responses (faster development and growth rate) and a higher mass at emergence were dependent upon the timing of cannibalism. Responses were more pronounced or only present if cannibalism occurred early in the larval period. 3. Our data suggest that cannibalism may not only act as a lifeboat mechanism by enabling cannibals to survive detrimental ecological conditions, but may also act as a compensatory mechanism to keep life history variables near‐optimal at life history transitions, even under sub‐optimal conditions.     

Experimental manipulation of tail length in female barn swallows (Hirundo rustica) affects their future reproductive success

Previous studies have shown no significant effect of experimentaltail length manipulation in female barn swallows (Hirundo rustica)at the beginning of a breeding season on reproductive successor behavior during that breeding season. In the present study,we investigate if tail length manipulation had any effect onreproductive performance the following year, the so-called long-termeffect, in contrast to the short-term effects already studied.We found that females with experimentally elongated externaltail feathers at the beginning of a breeding season producedless offspring during the breeding season the following yearthan did females with shortened or unmanipulated tails. Theseresults suggest that tail elongation caused flight deficienciesthat deteriorated the condition of females and eventually reducedreproductive success. The finding of long-term effects but nosignificant short-term effects for female tail elongation suggeststhat female barn swallows have the ability to adjust immediateparental investment. Detrimental effects of long tails in femalesin terms of decreased reproductive success might explain whyfemale tails are not as long as those of males. Finally, femalesmated to long-tailed (sexually attractive) males decreased theirreproductive success the following year more than did femalesmated to short-tailed males, possibly owing to differentialparental effort causing a deterioration of their condition.     

Reproductive tradeoffs and yolk steroids in female leopard geckos, Eublepharis macularius

Life history theory predicts tradeoffs among reproductive traits, but the physiological mechanisms underlying such tradeoffs remain unclear. Here we examine reproductive tradeoffs and their association with yolk steroids in an oviparous lizard. Female leopard geckos lay two eggs in a clutch, produce multiple clutches in a breeding season, and reproduce for several years. We detected a significant tradeoff between egg size and the number of clutches laid by females during their first two breeding seasons. Total reproductive effort was strongly condition-dependent in the first season, but much less so in the second season. Although these and other tradeoffs were unmistakable, they were not associated with levels of androstenedione, oestradiol, or testosterone in egg yolk. Female condition and egg size, however, were inversely related to dihydrotestosterone (DHT) levels in egg yolk. Finally, steroid levels in egg yolk were not directly related to steroid levels in the maternal circulation when follicles were developing, indicating that steroid transfer to eggs is regulated. These findings suggest that maternal allocation of DHT could mitigate tradeoffs that lead to poor offspring quality (i.e. poor female condition) and small offspring size (i.e. small egg size).