Are the two physiological races of Pollicipes polymerus (Cirripedia) genetically divided along the California coast?

Abstract. Genetic work on numerous species with planktonically dispersing larvae has demonstrated gene flow throughout populations along the California coast, despite steep environmental gradients around Point Conception. Previous ecological work on a planktonically dispersing intertidal barnacle, Pollicipes polymerus , demonstrated that this species is divided into two physiological races near Point Conception, at Point Latigo. The northern race broods when water temperature either warms or cools to 14°C and the southern race broods as water warms to 20°C. I examined 8 polymorphic allozyme loci from five populations between Santa Cruz and San Diego to test if the two physiological races are genetically divided. No genetic differences were found over this geographic range, supporting a previous molecular study. These results suggest that reproductive differences between the two races of this stalked barnacle may result from plasticity in brooding activity.     

Effectiveness of the caudal spine as a defense mechanism in Keratella cochlearis

The temporal distribution of spined and unspined forms of Keratella cochlearis in Cubillas reservoir during an annual cycle, and the stomach contents of Asplanchna girodi, were studied. The results suggest that the length of the caudal spine plays a critical role in the defense against predation by Asplanchna girodi. Short-spined forms showed a higher susceptibility to predation than unspined forms, which may have important consequencies for spine length variation in Keratella cochlearis populations.     

Morphological and behavioral defenses in dragonfly larvae: trait compensation and cospecialization

Many animals have two basic traits for avoiding being killedby a predator: behavioral modification and morphological defense.We examined the relationship between antipredator behavior andmorphological defense in larvae of three closely related dragonflyspecies within the genus Leucorrhinia. The three species differwith regard to their morphological defense as expressed in thelength of the larval abdominal spines. Results showed that longerabdominal spines provided protection against an attacking fishpredator (perch) because the probability of being rejected afteran attack was significantly higher in the species with the longestabdominal spines. In contrast to other studies, the specieswith the strongest morphological defense did not show the leastbehavioral predator avoidance. Instead, the species with intermediatemorphological defense showed the least predator behavioral avoidance.The results suggest that the Leucorrhinia system is a mixtureof trait cospecialization (a positive correlation between antipredatorbehavior and morphological defense) and trait compensation (anegative correlation between antipredator behavior and morphologicaldefense). Differences in the relationship between morphologicaland behavioral defense between species might be related to abundancepatterns of the three species in lakes with and without fishpredators.     

Sexual conflict over breeding substrate causes female expulsion and offspring loss in a cichlid fish

Females of the Lake Tanganyika cichlid Lamprologus callipterusexclusively breed in empty snail shells that males collect intheir territories. Male–male competition for shells issevere, leading to frequent shell stealing and territory takeover.As a consequence, males have breeding females in their shellsthat spawned with competitors. In this field study, we investigatedboth naturally occurring and experimentally induced encountersof territorial males with females that had spawned with othermales. We found that the breeding success of females that weretaken over by a different male was significantly reduced. Behavioralobservations after experimental shell relocation further showedthat males recognized females that they had not spawned with:males directed more exploration and manipulation behavior towardsuch shells compared with controls. Reoccupation rate of emptiedexperimental shells was significantly higher than that of unmanipulatedempty shells. This indicates that shell stealing and nest takeover,followed by female expulsion, contribute to the reproductivesuccess of L. callipterus males. We also found that female matechoice reduces expulsion risk: females preferred to mate withlarge males, and male size correlated with dominance. We concludethat the limited availability of breeding substrate is a keydeterminant of both intrasexual competition and intersexualconflict in this species.     

Antennule shape and body size of <Emphasis Type="Italic">Bosmina</Emphasis>: key factors determining its vulnerability to predacious Copepoda

Cyclopoid copepods are common in lakes and ponds, and they have a significant predation impact on the communities of the small zooplankton species. To reduce the predation risk, some cladoceran zooplankters develop protuberant (defensive) morphologies in the presence of the copepods. In the case of the small cladoceran Bosmina, they elongate their appendages (antennule and mucrone) and change the antennule morphotype. However, information about the effectiveness of these defensive devices against copepod predation is still insufficient. In our study, to find the compositive effects of these appendages on the vulnerability of Bosmina, we exposed two bosminid species (B. longirostris and B. fatalis) of different body sizes and with appendages of different lengths and shapes to copepod (Mesocyclops) predation. The experiment revealed that the shape of the antennule is a main factor determining the bosminid’s vulnerability to copepod predation and indicated that the protection of the opened ventral carapace must be a key strategy by which Bosmina avoids copepod predation.     

再引入黑颈长尾雉育雏行为和育雏地选择

2004～2005年在广西岑王老山自然保护区对再引进黑颈长尾雉的育雏行为和育雏地选择进行了研究.结果表明:雏鸟活动能力随时间明显增强,1～3日活动面积在300 m2以内.育雏初期为地栖,后期开始为树栖.育雏地有3种类型:人工西南桦幼林、针叶林、针阔混交林.3种生境的乔木盖度分别是75%、90%、85%;草本盖度分别是80%、60%、65%.Mann-Whitney U分析表明草本层盖度,水源距离,林缘距离,林间小路距离是影响黑颈长尾雉育雏地选择的主要因子.     

Experimentally-elevated testosterone, female parental care, and reproductive success in a songbird, the Dark-eyed Junco (Junco hyemalis)

In male dark-eyed juncos (Junco hyemalis), experimentally elevated testosterone (T) decreases male parental care and offspring survival, but results in higher overall fitness through greater mating success. To help address the ensuing question of what prevents selection from favoring higher levels of T in male juncos, we manipulated T in female juncos. A previous study demonstrated no effect of experimentally elevated T on female incubation behavior, suggesting that female parental behavior might be insensitive to T. In this study we asked whether experimentally elevated T mediates other female parental behaviors and whether variation in T-mediated parental behavior might influence reproductive success. We videotaped free-living control- and T-females during nesting to quantify brooding behavior when young were 3 days old and provisioning behavior when young were 6 days old. Nest defense was measured by quantifying responses to a mounted predator placed near the nest. Reproductive success was assessed via fecundity, nestling quality, and nest survival. T-females spent less time than control females brooding but did not differ in provisioning rate. T-females performed fewer dives at the predator mount and, unlike controls, failed to increase defense as nesting progressed. T-females also had lower daily nest survival and lower nest success (odds of producing at least one fledgling). We conclude that some aspects of female parental behavior are sensitive to experimentally elevated T while others are not and consider the implications for the evolution of T-mediated characters in both sexes.     

Pyrrolizidine alkaloid deters ant predators of Utetheisa ornatrix eggs: effects of alkaloid concentration,oxidation state,and prior exposure of ants to alkaloid-laden prey

To examine the chemical defense of lepidopteran eggs towards ant predators, eggs of the arctiid moth Utetheisa ornatrix were offered to laboratory colonies of the ant Leptothorax longispinosus. The ants rapidly devoured Utetheisa eggs produced by parents reared on an alkaloid-free diet, but left eggs that had been endowed with parental alkaloid largely unmolested. That defense can be attributed directly to the presence of a pyrrolizidine alkaloid since topical application of monocrotaline in either its free base or N-oxide state conferred protection on otherwise palatable eggs. The N-oxide and free base were not equally effective in conferring protection however; free-base treated eggs were subject to greater predation than N-oxide treated eggs after 24 h. The emergence of differential alkaloid effectiveness only after prolonged exposure is consistent with the notion that chemical protection is seldom absolute. That difference was resolved only when the otherwise food-deprived ants exceeded a certain threshold of hunger. The efficacy of applied monocrotaline as a predator deterrent increased with increasing concentration of N-oxide, but was lowest for eggs treated with an intermediate concentration of free base. The latter concentration effect likely represents an artefact of the behaviour of the ant colonies offered eggs treated with an intermediate concentration, as those colonies were the most voracious predators in reference tests with palatable eggs. In addition to the immediate deterrent value of pyrrolizidine alkaloid, ant colonies that had been exposed to alkaloid-laden eggs subsequently avoided even palatable, unprotected eggs offered 33 days later. Our data provide the first demonstration of such long-term avoidance of chemically protected lepidopteran prey by an invertebrate. The discovery of a mechanism promoting learned avoidance on the part of ant predators has important ramifications to egg-laying strategies of female Utetheisa, both in terms of the dispersion of eggs, and the extent to which eggs are provisioned with alkaloid.