Jürg Lamprecht

Female-biased immigration and male peace-keeping in groups of the shell-dwelling cichlid fish Neolamprologus multifasciatus

Abstract The small cichlid fish Neolamprologus multifasciatus is endemic to Lake Tanganyika and is unique among fish because it lives in complex social groups with several reproductive males and females, all of which participate in defending their territory against neighbors and intruders. Individuals use empty snail shells for breeding and shelter. Previous parentage analysis using microsatellites suggested occasional exchange of individuals between groups. In field experiments, we found that females showed a higher tendency than males to migrate into territories already occupied by a resident pair. The phenomenon and causes of female-biased immigration were further investigated in aquarium experiments: Nine of 15 females, but only 2 of 15 equally sized males, settled in territories of established pairs. Territorial males exhibited more aggression toward strange males (potential reproductive competitors) than toward strange females (potential additional mates); their females were more aggressive toward strange females (probably competitors for shells) than toward strange males. Apparently, a conflict exists between the sexes regarding the immigration of additional females. This conflict seems to be the selective basis for observed active male interference in aggressive disputes between females in the territory. Interfemale tolerance in a group was greater in the male’s presence than in his absence.

The importance of biparental care in a precocial, monogamous bird, the bar-headed goose (Anser indicus)

SummaryThis study presents the first direct evidence of benefit derived from the males parental effort during rearing of young in a monogamous, precocial bird species. We compared mothers accompanied by a mate (paired mothers) with single mothers, some of which were artificial widows, in a semicaptive flock of bar-headed geese (Anser indicus). Paired mothers were less often displaced by other birds and suffered fewer interruptions of brooding. Their goslings spent more time grazing and survived with a higher probability. Although one beneficial result of the males parental effort may be the continued availability and survival of his mate, a more direct benefit arises from higher offspring survival between hatching and fledging.

Factors influencing pairbond stability in convict cichlids (Cichlasoma nigrofasciatum)

In isolated pairs of the biparental convict cichlid (Cichlasoma nigrofasciatum) caring for fry, pairbonds can be broken by removal of the fry. Within three hours, the mates of many pairs become so mutually aggressive that the female finally flees from her larger mate, who chases her. The pairbond is mended within seconds upon re-introduction of the fry. Yet removal of young leaves some pairs little or not at all affected. They seem to have more stable pairbonds. Multiple regression of data from 39 pairs on a quantitative measure of pairbond destruction revealed support for the so-called parity-hypothesis, which holds that a cichlid pair is compatible only when the females aggressiveness compensates for her smaller size. The size of the female relative to the males, and her aggressiveness relative to his in the undisturbed situation, proved positive predictors of pair stability in the fry stage. Thus the same factors which have earlier been shown to favour pair formation in other biparental cichlids seem also responsible for pair stability in a later stage of the reproductive cycle.

Distress call alternation in hand-reared goslings (Anser-indicus) - vocal co-operation between siblings

Abstract Hand-reared bar-headed goslings ( Anser indicus ) isolated in pairs tend to alternate their distress calling. This phenomenon has earlier been reported for ducklings by other authors, who suggested a co-operative function in attracting the parent(s). In this paper six possible functions are considered: co-operation between siblings; non-interference (not calling when other sounds interfere with the signal); orientation response (listening to other sounds); calm down response (reducing arousal when sounds are heard); approach response (approach instead of calling when parent calls); and fear response (inhibition of calling when fear-provoking stimuli are heard). Playback experiments showed that the goslings alternated more with some low-frequency sounds (electric buzzer, adult excitement calls) than with the much higher distress calls of siblings or other goslings, which were the most attractive for parent geese. When silent, the subjects increased locomotion and did not show listening behaviour. The results seem most compatible with a fear response function, and it is suggested that alternation with siblings might be an artifact. Difficulties in measuring the alternation tendency are discussed.

Dominanz und Fortpflanzungserfolg bei Streifengänsen (Anser indicus): Eine multiple Regressionsanalyse

Die positive Korrelation zwischen der Ranghöhe eines Paares im Winter und seinem Fortpflanzungserfolg (Anzahl flügge Junge) im nächsten Sommer wurde bei zahmen, freifliegenden Streifengänsen (Anser indicus) daraufhin untersucht, ob die Dominanz nicht lediglich ein Nebeneffekt einer anderen möglichen Ursache des Fortpflanzungserfolges ist. Untersucht wurden ♂-Alter, ♀-Alter, ♂- und ♀ -Gewicht im Januar sowie Anzahl der Jungen im Vorjahr. Eine multiple Regressionsanalyse zeigte, daß die Dominanz einen positiven Bezug zum Fortpflanzungserfolg auch dann behielt, wenn die anderen Variablen konstant gehalten wurden. Von den anderen ließ nur das ♂ -Alter in einem Jahr eine nennenswerte Beziehung zur Fortpflanzungserfolg erkennen. Eine zusätzliche Analyse, bei der die Verpaarungsdauer mit berücksichtigt wurde, ergab, daß die Korrelation zwischen Dominanz und Erfolg auch nicht über diesen Faktor zu erklären ist. Die Möglichkeit, daß die Dominanz den Fortpflanzungserfolg beeinflußt, und die Wege, über die das geschehen könnte, werden diskutiert. Bei hoher Nesterdichte scheint der Einfluß der Dominanz besonders stark zu sein. A positive correlation between the dominance rank of a pair in winter and its reproductive success (number of young fledged) in the following summer was found in a semi-captive flock of Bar-headed geese. The possibility that dominance was simply a side-effect of other possible causes of reproductive success (male and female age, male and female weight in January, or number of young fledged in the previous year) was tested. A multiple regression analysis revealed that dominance was positively associated with reproductive success even when the other variables were held constant. Of the others, only male age showed some association with reproductive success in one year. A further analysis, including also pair bond duration, showed that the correlation between dominance and success could also not be explained by co-variation with this factor. The possibility that dominance influences reproductive success and the different ways in which this could be achieved are discussed. The influence of dominance seems strongest when nest density is high.