Influence of helping and breeding experience on reproductive performance in the Seychelles warbler: a translocation experiment

Reproductive success of the cooperative breeding Seychelleswarbler (Acrocephalus sechellensis) increases with age. Thisage effect is not due to differential survival or increasedreproductive effort, but to accumulated helping and breedingexperience. In their first year of breeding, reproductive performanceof inexperienced warblers with neither helping nor breedingexperience was significandy lower than that of warblers of thesame age with either previous helping or breeding experience.Reproductive performance was the same for primiparae with helpingexperience and for birds with breeding experience. Female primiparaewith helping experience or breeding experience built betternests and spent more time incubating than inexperienced females,which led to increased hatching success. Male primiparae withhelping experience or males with breeding experience guardedthe clutch better than inexperienced males, which led to reducedegg predation. Even-aged warblers with different previous experienceswere transferred to unoccupied islands, where birds startedbreeding immediately in high-quality territories. The experimentshowed that birds with helping experience produced their firstfledgling as fast as experienced breeders, and significandyfaster than inexperienced birds. Breeding performance did notimprove further with experience after the first successful breedingattempt. Only birds with previous breeding experience who pairedwith inexperienced birds, were likely to change mate. The otherpair combinations remained stable. Thus, primiparous birds withhelping experience have greater lifetime reproductive successthan inexperienced primiparae of the same age. This experimentshows that helping behavior has not only been selected for inthe context of promoting an individual's indirect fitness, butalso in the context of gaining helping experience which translatesinto improved reproductive success when a helper becomes a breeder.[Behav Ecol 7: 326-333 (1996)]     

Behavioral responses of a sex-role reversed pipefish to a gradient of perceived predation risk

Conspicuous behaviors such as courtship and mating often makeanimals susceptible to predation. When perceiving themselvesat an elevated level of risk, animals frequently reduce conspicuousbehaviors in tradeoff for a decrease in probability of beingpreyed upon. In the present study, we used two experiments toexamine the effect of perceived predation risk from cod (Gadusmorhud) on nonreproductive and reproductive behaviors in thesex-role reversed pipefish (Syngnathus typhle). In the firstexperiment, no differences due to predation risk were detectedin the nonreproductive behaviors of either males or females.In the second experiment, predation risk had significant effectson reproductive behaviors. Pipefish were allowed to court andcopulate at four different predation levels. We created predationlevels differing in perceived predation risk by controllingthe number of sensory modes through which pipefish could detectthe presence of a cod. As predation risk increased, pipefishcopulated and courted less frequently, swam alone (displayedand searched for conspecifics) less often, and waited longerbefore commencing courtship. These changes in behavior minimizedthe amount of time spent above the eelgrass and presumably reducedconspicuousness to visual predators. Pipefish also copulatedafter a smaller amount of courtship as predation risk increased,indicating that they may trade information concerning mate qualityfor a reduction in predation risk. No differences were foundin any response variable between males and females. The roleof operational sex ratios and intersexual competition in determiningwhich sex assumes greater costs in mate acquisition is questioned.     

Phylogenetic analysis of cytochromeb sequences in the dasyurid marsupial subfamily phascogalinae: Systematics and the evolution of reproductive strategies

We report DNA sequence variation in 861 bp of the mitochondrial cytochromeb gene from 10 species of the dasyurid marsupial subfamily Phascogalinae (including the New Guinean genusMurexia) and an outgroup planigale (Planigale ingrami). Phylogenetic analyses of these sequences indicate that (1) the subfamily consists of three major clades corresponding to (a)Phascogale, (b) AustralianAntechinus, and (c) New Guinean Antechinus andMurexia; (2) Antechinus habbema constitutes the earliest branch of the New Guinean clade; and (3); Antechinus melanurus and A. naso are sister species within the New Guinean clade. Among Australian antechnuses,A. stuartii andA. swainsonii are more closely related to each other than either is toA. flavipes, a result that is seemingly at odds with all previous systematic studies. Although resolution is limited, it appears thatAntechnius andMurexia species form a clade to the exclusion ofPhascogale. This relationship suggests that male semelparity is not a strong synapomorphy for Australian antechinuses and phascogales, despite its apparent physiological similarity in the two groups.To whom correspondence should be addressed.     

SEXUAL DIFFERENTIATION OF GRIFFITHSIA (CERAMIALES, RHODOPHYTA): NUCLEAR PLOIDY LEVEL OF MIXED-PHASE PLANTS IN G. JAPONICA1

Mixed-phase plants of Griffithsia japonica Okamura spontaneously occurred in a laboratory culture. Four female plants produced tetrasporangia and spermatangia in addition to their normal female reproductive structures (bisexual/mixed-phase plants), and four male plants produced tetrasporangia as well as spermatangia (male/mixed-phase plants). To determine the nuclear ploidy level of these mixed-phase plants, relative nuclear sizes of male, female, tetrasporangial, and mixed-phase plants were measured using a microscopic image analysis system. Haploid gametophytes could be distinguished from diploid tetrasporophytes by relative nuclear sizes, with the later having nuclei twice the size of the former. Relative nuclear sizes of the mixed-phase plants were similar to those of the haploid plants. Thus, the mixed-phase plants were determined to be haploid. Haploid mixed-phase plants of G. japonica have a potential to produce male, female and tetrasporangial reproductive structures. Sex determination models are discussed to explain "haploid" mixed-phase phenomena in red algae .     

Male larval nutrition in Choristoneura rosaceana (Lepidoptera: Tortricidae): an important factor in reproductive success

This study examines how Choristoneura rosaceana male quality, as determined by larval diet, age and mating history, affects the reproductive success of both sexes. While the size of the spermatophore produced at first mating increased linearly with male age, the frequency of mating was significantly higher for middle-aged males (2–4 days old) than younger (0–2 days old) or older (6–8 days old) individuals, when both sexes were fed on artificial diet. However, the duration of copulation was longer in couples with older than younger males. The observed age-related changes in spermatophore size had no significant effect on female longevity, fecundity or fertility, suggesting no direct relationship between male investment and spermatophore size under these experimental conditions. Different larval food sources (artificial diet, maple and hazelnut) did not affect the proportion of 2-day-old virgin males that mated; however, the proportion that remated was significantly higher for males reared on high-quality food (maple and artificial diet) than those on hazelnut, a poorer food source. There was a 5-fold decline in spermatophore size between the first and second matings on all diets, but female reproductive output was reduced by only 25%. In contrast, while the first spermatophore produced by males on hazelnut was 1.5 times smaller than those produced on maple and artificial diet, the fecundity of their mates was 40% less than those mated with high-quality virgin males. These results provide additional support to the idea that spermatophore size is not a valuable indicator of male quality. Most tethered females placed in the field during the first flight period mated with virgin males (based on the size of the spermatophore), suggesting that female choice exists in this species. These results are discussed in relation to the incidence of polyandry in naturally occurring populations of Choristoneura and the potential use of size and/or chemical cues by females to assess male quality.     

Physiological energetics of the zebra musselDreissena polymorpha in lakes I. Growth and reproductive effort

Shell growth of tagged zebra mussels (Dreissena polymorpha) was monitored in lakes at 3 sites over 1 1/2 years. It varied greatly with the season and was almost absent during winter months. Shell growth was significantly correlated with seston concentration, but not with water temperature. The theoretical maximum size (L∞) of the v. Bertalanffy growth equation did not vary seasonally. Tissue weight underwent a pronounced seasonal cycle. In animals of 20 mm shell length, minimum weights recorded in September only corresponded to one quarter to one third of the maxima in late spring. Tissue weight of animals from the 3 sites was distinctly different. Carbohydrate content of the tissue stayed below 10 per cent and tended to be highest in spring. Spring maxima of lipids were very pronounced. These lipids were primarily located in the digestive gland. These data were combined with data of gonad size by Borcherding (1991). Results imply that production of reproductive tissue even continues at a retarded rate during winter months, if food conditions were favourable. With poor food conditions, no production of reproductive tissue was estimated during winter; this, however, was followed by an elevated rate of reproductive tissue production in spring. Weight specific production decreased with a weight exponent of −0.24. Shell and byssus production contributed only in the range of 10 per cent to total production. Reproductive effort showed maxima of 30 to 45%. It increased with shell length at 2 sites and decreased at the other site with the largest animals.     

Parasites, aggression and dominance in male upland bullies

The effects of the digenean trematode parasite Telogaster opisthorchis on aggression and competitive ability in male upland bullies ( Gobiomorphus breviceps ) were examined using mirror-image stimulation (MIS) techniques and dyadic contests for nest sites between pairs of males. Parasite load had no significant effect on male aggression or success in dyadic contests, nor was aggression a predictor of the likely winner of these contests. The results are discussed with relation to the role of parasites in male-male competition and to possible problems in using MIS techniques for studies on dominance and aggression in fish.     

Seasonal migration promoting assortative mating in Littorina brevicula on a boulder shore in Japan

Littorina brevicula Philippi is one of the most common snails found in the upper intertidal zone of Japan. In Amakusa, some of the population of L. brevicula migrate to the lower zone in the winter, while the rest stay in the upper zone. Thus, during the winter, which is its reproductive season, the population of L. brevicula divides into two sub-populations. This leads to a hypothesis that the migration pattern in winter is genetically controlled and this behavioural dimorphism is maintained by reproductive isolation between the two sub-populations. In order to test this hypothesis, the following three points were investigated: (1) whether the same snails migrate in a similar way every winter, (2) whether there is a significant tidal level preference in snails, and (3) whether reproductive isolation occurs between the two sub-populations. The results showed (1) the migration behaviour of each snail was consistent over two successive winters, i.e. the same group of snails migrated downward every winter and the same group of snails stayed in the upper zone every winter, (2) transplanted snails moved toward the original zones where they were caught, suggesting that the snails actively selected their tidal zone in winter, and (3) most of the snails copulated within each sub-population. Therefore, reproductive isolation between the two sub-populations was considered to be established to some extent by the dimorphic migration behaviour. In conclusion, the migratory behaviour of L. brevicula is determined separately for each individual and might be genetically controlled, and the behavioural dimorphism may be maintained by partial reproductive isolation between the two sub-populations.