Scott Creel

Communal hunting and pack size in African wild dogs, Lycaon pictus

Abstract African wild dogs are 20–25 kg social carnivores whose major prey are ungulates ranging from 15 to 200 kg. In the Selous Game Reserve, Tanzania, wild dog pack size ranged from three to 20 adults (3–44 including yearlings and pups). Data from 905 hunts and 404 kills showed that hunting success, prey mass and the probability of multiple kills increased with number of adults. Chase distance decreased with number of adults. None the less, the distribution of per capita food intake across adult pack size was U-shaped, with a minimum close to the modal pack size. A similar result has been used to conclude that cooperative hunting does not favour sociality in lions (Packer et al. 1990, Am. Nat., 136, 1–19), and to argue that cooperative hunting is not responsible for group living in any carnivore (Caro 1994, Cheetahs of the Serengeti Plains: Group Living in an Asocial Species). Daily per capita food intake only accounts for variation in the benefits to cooperative hunting, ignoring variation in costs. For Selous wild dogs, per capita food intake per km chased peaked close to the modal adult pack size (where per capita food intake per day was near its minimum). Thus, the energetics of cooperative hunting favour sociality in Selous wild dogs. Analyses that incorporate variation in both costs and benefits of hunting may show that cooperative hunting favours sociality in other species where its influence has previously been rejected.

Behavioural and endocrine mechanisms of reproductive suppression in Serenge dwarf mongooses

Behavioural, demographic and endocrine data were collected from a wild population of dwarf mongooses, Helogale parvula, in Serengeti National Park, Tanzania. The data show that subordinate females are reproductively suppressed by a complex of endocrine and behavioural mechanisms, while subordinate males are reproductively suppressed primarily by behavioural mechanisms. Subordinate females have (1) low baseline oestrogen levels, (2) low mating rates, and (3) low peak oestrogen levels during mating periods. Subordinate males (1) have low mating rates, and (2) are the recipients of increased aggression during mating periods, but (3) have androgen levels indistinguishable from those of dominants, both during and away from mating periods. Mechanistic differences between the sexes suggest that the selection pressures favouring reproductive suppression may also differ between the sexes.

Cooperative hunting and group size: assumptions and currencies☆

No abstractCopyright 1997 The Association for the Study of Animal Behaviour1997The Association for the Study of Animal Behaviour

Steroid metabolism and validation of noninvasive endocrine monitoring in the African wild dog (Lycaon pictus)

The purpose of this study was to validate noninvasive endocrine monitoring techniques for African wild dogs (Lycaon pictus) and to establish physiological validity of these methods by evaluating longitudinal reproductive-endocrine profiles in captive individuals. To determine the primary excretory by-products of ovarian steroid metabolism, [14C]-progesterone and [3H]-estradiol were co-administered to a female and all excreta were collected for 80 hr postinjection. Radiolabel excretion peaked ≤ 18 hr postinfusion, and progesterone and estradiol metabolites were excreted in almost equivalent proportions in urine (39.7 and 41.1%, respectively) and feces (60.3 and 58.9%, respectively). Most of the urinary metabolites were conjugated (estradiol, 94.3 ± 0.3%; progesterone, 90.4 ± 0.5%), so that immunoassays for pregnanediol-3α-glucuronide (PdG) and estrogen conjugates (EC) were effective for assessing steroid metabolites. Two immunoreactive estrogens (estradiol and estrone) and at least one immunoreactive progesterone metabolite (3α-hydroxy-5α, pregnan-20-one) were detected in feces. Urine and fecal samples were collected (1–3 times per week) for 1.5 yr from one adult female and two adult males to assess longitudinal steroid metabolite excretion. Overall correlation of urinary PdG to matched, same-day fecal progesterone metabolites immunoreactivity was 0.38 (n = 71, P < 0.05). Similarly, urinary EC was correlated (P < 0.05) with same-day fecal estrogen immunoreactivity (r = 0.49, n = 71). During pregnancy and nonpregnant cycles, copulation occurred at the time of peak (or declining) estrogen metabolites and increasing progesterone metabolites concentrations. Estrus duration was 6–9 days and gestation lasted 69 days with parturition occurring coincident with a drop in progesterone metabolites. Males exhibited seasonal trends in fecal testosterone excretion with maximal concentrations from July to September coincident with peak mating activity. Although these limited longitudinal hormone profiles should be interpreted cautiously, noninvasive gonadal steroid monitoring suggests that: (1) both female and male wild dogs may exhibit reproductive seasonality in North America, (2) females are monoestrous, and (3) peak testicular activity occurs between August and October coincident with mating behavior. From a conservation perspective, noninvasive endocrine monitoring techniques should be useful for augmenting captive breeding programs, as well as for developing an improved understanding of the physiological mechanisms underlying reproductive suppression in response to social and ecological pressures. Zoo Biol 16:533–548, 1997.

How to Measure Inclusive Fitness

Although inclusive fitness (Hamilton 1964) is regarded as the basic currency of natural selection, difficulty in applying inclusive fitness theory to field studies persists, a quarter-century after its introduction (Grafen 1982, 1984; Brown 1987). For instance, strict application of the original (and currently accepted) definition of inclusive fitness predicts that no one should ever attempt to breed among obligately cooperative breeders. Much of this confusion may have arisen because Hamilton’s (1964) original verbal definition of inclusive fitness was not in complete accord with his justifying model. By re-examining Hamilton’s original model, a modified verbal definition of inclusive fitness can be justified.

Pregnancy, oestrogens and future reproductive success in Serengeti dwarf mongooses

Social subordinates do not normally reproduce in most communally breeding birds, mammals and insects (Abbott 1987; Brown 1987; Queller & Strassman 1989; Creel & Waser 1991). Occasional reproduction by subordinates of such species is often implicitly regarded as random failure of the typical pattern of reproductive suppression (e.g. Kleiman 1977). In this note, we use endocrine and demographic data from free-living dwarf mongooses, Helogale parvula, to show that pregnancy among subordinates was followed by long-term elevations of baseline oestrogen levels. This elevation of baseline oestrogens persisted in the first year after attaining dominance. Peak oestrogens during oestrus periods were also higher in multiparous than in primiparous first-year dominants. Multiparous first-year dominants had a shorter interval between attaining dominance and becoming pregnant, a higher probability of giving birth in their first season of dominance, and greater reproductive success. Thus, through persistent endocrine effects, pregnancy can be evolutionarily favoured even if it does not immediately yield surviving offspring. Dwarf mongooses are small, communally breeding carnivores. In our study population in Serengeti National Park, pack size ranged from two to 21 adults (x* s~=8.9+0.4, N=202; Rood 1980; Creel et al. 1992). The population was under behavioural and demographic study from 1974 to 1991, with endocrine and genetic data collected from 1987 to 1991. Social dominance was tightly correlated with age (Rood 1980; Creel et al. 1992)

The future components of inclusive fitness: accounting for interactions between members of overlapping generations.

Abstract Indirect fitness is the portion of an individuals inclusive fitness due to the effects of the individuals behaviour on the reproductive value of non-descendant kin. Indirect fitness may play a role in the evolutionary maintenance of cooperative breeding, in which some individuals help others to breed. Recently, theoretical and empirical studies have addressed the future component of indirect fitness, i.e. the effects of an individuals current behaviour on the subsequent survival and reproduction of nondescendant kin. A difficulty in accounting future fitness effects arises when generations overlap in a cooperative breeding system (as is normally the case). Individuals of one generation can serve as helpers to individuals of the previous generation, ‘returning from the future’ to compound their ancestors fitness. This paper classifies the types of fitness effects arising from generational interactions in cooperative breeding systems. This classification is then used to suggest methods of measuring future indirect and future direct (individual) fitness so that they are directly comparable.