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R Heinsohn

Publications and source records attributed to R Heinsohn.

9 recordsLinked to original sources
PubMed2006

Cryptic gentes revealed in pallid cuckoos Cuculus pallidus using reflectance spectrophotometry.

Many cuckoo species lay eggs that match those of their hosts, which can significantly reduce rejection of their eggs by the host species. However, egg mimicry is problematic for generalist cuckoos that parasitize several host species with different egg types. Some generalist cuckoos have overcome this problem by evolving several host-specific races (gentes), each with its own, host-specific egg type. It is unknown how generalist cuckoos lacking gentes are able to avoid egg rejection by hosts. Here we use reflectance spectrophotometry (300-700 nm) on museum egg collections to test for host-specific egg types in an Australian generalist cuckoo reported to have a single egg type. We show that the colour of pallid cuckoo (Cuculus pallidus) eggs differed between four host species, and that their eggs closely mimicked the eggs of the host they parasitized. These results reveal that pallid cuckoos have host-specific egg types that have not been detected by human observation, and indicate that gentes could be more common than previously realized.

Adaptation, Physiological↗
PubMed2000

Coalitions of relatives and reproductive skew in cooperatively breeding white-winged choughs.

We used DNA fingerprinting to examine reproductive skew in cooperatively breeding white-winged choughs, Corcorax melanorhamphos, which live in groups of up to 20 individuals. Before a severe drought, groups that had been stable for multiple years were characterized by long-term monogamy involving a single breeding pair (high skew). After the drought, new groups formed from the amalgamation of multiple individuals and coalitions of relatives. At most one member of each faction succeeded in breeding, such that skew was dependent on the number of unrelated factions, and not group size. In the new groups, dominant males and females with supporting relatives were always successful. Whereas most females without support also gained breeding positions, many males without family support failed to breed. Thus subordinates gain indirect fitness by first helping related males to secure a breeding position, and then helping to raise their young. Our study demonstrates the advantage of operating in coalitions, and suggests that the acquisition of future allies may be a major benefit of helping behaviour in this species.

Animals↗
PubMed1999

The cost of helping.

Cooperative breeding in mammals, birds and fish has provided evolutionary biologists with a rich framework for studying the causes and consequences of group-based reproduction. Helping behaviour is especially enigmatic because it often entails an individual sacrificing personal reproduction while assisting others in their breeding attempts. The decision to help others to reproduce is affected by immediate and future costs analogous to those of direct reproduction, but these components of the equation have usually been neglected. Recent research suggests that the type of benefit sought could determine the extent of help given.

Journal Article↗
PubMed1997

Group territoriality in two populations of African lions

Lionesses, Panthera leoin the Serengeti ecosystem, Tanzania, assess the odds of winning group-territorial contests by counting the number of opponents they hear roaring. They will approach intruders aggressively only if they outnumber them. Here the lionesses in the Serengeti are compared with another population living nearby but in strikingly different ecological circumstances. The lions of Ngorongoro Crater live at much higher densities owing to year-round availability of non-migratory prey species, but also suffer higher mortality from fighting. Playback experiments showed that lionesses in the crater differ from those in the Serengeti by approaching 'intruders' more quickly when the odds of winning are low. This increased aggression is interpreted in terms of the greater difficulty of holding a territory at high population density.

Journal Article↗
PubMed1996

Development of cooperative territoriality in juvenile lions.

African lions, Panthera leo, engage in many cooperative activities including hunting, care of young, and group territoriality, but the contribution of juvenile lions to these activities has never been documented. Here we present experimental evidence that juvenile lionesses make a gradual transition to group-territorial defence between weaning (8 months) and sexual maturity (42 months). When challenged by simulated intruders played from a loud-speaker, juvenile females (but not males) become progressively more likely to join the adult females in territorial defence with age, and their behaviour is affected by both the number of defending adults and the number of intruders. We interpret the ability of juveniles to assess relative numbers as an adaptation for assessing the risk of territorial conflict according to their own fighting ability, and the ability of their pride of successfully defend the territory. The difference between the sexes reflects the greater value of the natal territory to philopatric females. Adult females display a variety of strategies when defending the territory, including unconditional and conditional forms of cooperation. We show here that individuals display the rudiments of these strategies as juveniles.

Animals↗
PubMed1995

Complex cooperative strategies in group-territorial African lions.

Female lions (Panthera leo) showed persistent individual differences in the extent to which they participated in group-territorial conflict. When intergroup encounters were simulated by playback of aggressive vocalizations, some individuals consistently led the approach to the recorded intruder, whereas others lagged behind and avoided the risks of fighting. The lead females recognized that certain companions were laggards but failed to punish them, which suggests that cooperation is not maintained by reciprocity. Modification of the "odds" in these encounters revealed that some females joined the group response when they were most needed, whereas other lagged even farther behind. The complexity of these responses emphasizes the great diversity of individual behavior in this species and the inadequacy of current theory to explain cooperation in large groups.

Africa↗
PubMed1987

Computer-aided hybridoma screening. Production of monoclonal antibodies against membrane fractions from mammary tumour tissue.

Monoclonal antibodies were raised against membrane fractions from mammary tumour tissue. 746 hybridomas were obtained against the so-called membrane fraction '2a' and 1393 hybridomas against the so-called 'top-region'. These hybridomas were tested with an immunodot assay, cell-binding radioimmunoassay and an immunocytological screening assay using several antigens. In the evaluation of these data we used the common database software (dBASE II) on a personal computer. To facilitate computer handling, even for the non-specialist, we programmed our individual menu-driven software for computer-aided hybridoma screening.

Animals↗
PubMed1987

Screening of hybridoma supernatants raised against membrane fractions from breast cancer using an immunodot assay.

Membranes were prepared from mammary tumors and fractionized using gel filtration and gradient polyacrylamide gel electrophoresis. To obtain monoclonal antibodies against tumor-associated antigens, mice were immunized against membrane fraction 2a. After hybridization, we obtained 746 hybridoma cell lines. We performed the immunodot assay for screening. Every supernatant was tested against 15 antigens. Eight antigens were purified fractions from tumor membrane preparation, and five were crude membrane preparations from benign and malignant breast cell lines. Additionally, the Thomsen-Friedenreich antigen of erythrocytes was tested. We selected 83 hybridomas for further characterization.

Animals↗