Abstract: A fundamental goal of sociobiology is to explain how complex social behaviour evolves, especially in social insects, the exemplars of social living. Although still the subject of much controversy, recent theoretical explanations have focused on the evolutionary origins of worker behaviour (assistance from daughters that remain in the nest and help their mother to reproduce) through expression of maternal care behaviour towards siblings. A key prediction of this evolutionary model is that traits involved in maternal care have been co-opted through heterochronous expression of maternal genes to result in sib-care, the hallmark of highly evolved social life in insects. A coupling of maternal behaviour to reproductive status evolved in solitary insects, and was a ready substrate for the evolution of worker-containing societies. Here we show that division of foraging labour among worker honey bees (Apis mellifera) is linked to the reproductive status of facultatively sterile females. We thereby identify the evolutionary origin of a widely expressed social-insect behavioural syndrome, and provide a direct demonstration of how variation in maternal reproductive traits gives rise to complex social behaviour in non-reproductive helpers.

Abstract: There are two distinct types of social organization and, accordingly, two types of mating systems in equids. In the horse, Plains zebra and Mountain zebra, the adults live in non-territorial and cohesive one-male groups and in stallion groups. The family stallions have exclusive mating rights which are respected by all others. In Grevy's zebra and in the African and Asiatic wild asses, the stallions are permanently territorial and have exclusive mating rights within their territories. Ecological and evolutionary aspects are discussed.

Abstract: Many large mammals show pronounced seasonal fluctuations of metabolic rate (MR). It has been argued, based on studies in ruminants, that this variation merely results from different levels of locomotor activity (LA), and heat increment of feeding (HI). However, a recent study in red deer (Cervus elaphus) identified a previously unknown mechanism in ungulates--nocturnal hypometabolism--that contributed significantly to reduced energy expenditure, mainly during late winter. The relative contribution of these different mechanisms to seasonal adjustments of MR is still unknown, however. Therefore, in the study presented here we quantified for the first time the independent contribution of thermoregulation, LA and HI to heart rate (f(H)) as a measure of MR in a free-roaming large ungulate, the Przewalski horse or Takhi (Equus ferus przewalskii Poljakow). f(H) varied periodically throughout the year with a twofold increase from a mean of 44 beats min(-1) during December and January to a spring peak of 89 beats min(-1) at the beginning of May. LA increased from 23% per day during December and January to a mean level of 53% per day during May, and declined again thereafter. Daily mean subcutaneous body temperature (T(s)) declined continuously during winter and reached a nadir at the beginning of April (annual range was 5.8 degrees C), well after the annual low of air temperature and LA. Lower T(s) during winter contributed considerably to the reduction in f(H). In addition to thermoregulation, f(H) was affected by reproduction, LA, HI and unexplained seasonal variation, presumably reflecting to some degree changes in organ mass. The observed phase relations of seasonal changes indicate that energy expenditure was not a consequence of energy uptake but is under endogenous control, preparing the organism well in advance of seasonal energetic demands.

Abstract: Over a 16-year period (1979-1994), long-term investigations were carried out on 14 Misaki feral stallions to analyze changes in harem size and the reproductive success. Harem size changed with the age of the stallions. Most stallions formed harem groups with four to five mares at the age of 4-6 and then the number of mares increased rapidly to the maximum at the age of 6-9 years. Thereafter, harem size decreased gradually to a minimum with advancing age. The harem size of 60 stable harem groups ranged from 1 to 9, and the average varied from a minimum mean of 1.8 in 1988 to a maximum mean of 5.3 in 1982. Mean harem size increased as adult sex ratio increased and a significant and positive correlation was found between them. One hundred and ninety-eight sire-foal pairs were determined by a paternity test with blood types and consort relations between stallions and mares during the study period. Out of 99 foals which were born in the stable harem groups, the true sires of 84 foals (85%) were the harem stallions in which the foals were born but the remaining 15 foals (15%) were sired by other harem stallions. Two out of three stallions which were studied throughout their lifetime produced 24 and 25 foals in 10 and 11 years of their reproductive lifespan, respectively. Another one produced only five foals in 6 years. The number of foals sired by the harem stallions was less than two over harem size 7 and some of the foals born in the harem were sired by other harem stallions. These results suggest that if a particular stallion monopolizes too many mares, he could not sire so many offspring because he could not always prevent his rival stallions from mating with his mares in wild or feral circumstances.