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R. P. MICHAEL and D. ZUMPE

Summary.

The frequency of ejaculation in thirty-two pairs of rhesus monkeys studied during seventy-five menstrual cycles was significantly higher (P<0·001) in the follicular than in the luteal phase of the cycle: this pattern was closely similar to the changes in the incidence of sexual intercourse reported in a human population.

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R. P. Michael and R. W. Bonsall

Like many other non-human primates (Lancaster & Lee, 1965; Michael & Zumpe, 1971), rhesus monkeys in the wild (Vandenbergh & Vessey, 1968) and in captivity (Michael & Keverne, 1971; Michael, Zumpe, Plant & Evans, 1975; Robinson, Scheffler, Eisele & Goy, 1975) exhibit seasonal changes in sexual behaviour. In the northern hemisphere there is a peak in ejaculatory activity in the late autumn and early winter followed by a decline in late winter and spring when, in the wild, most fertile females are pregnant. However, pregnancy is not the sole cause of the decline in sexual activity. Pairs of intact monkeys in which the females were sterilized by ligation of the oviducts (Michael & Keverne, 1971) and pairs in which the females were ovariectomized and treated s.c. with 10 μg oestradiol benzoate/day (Michael et al., 1975) showed the seasonal changes characteristic of intact animals in the wild. It seemed, therefore, that the annual behavioural rhythm might be in part dependent on changes within the male of the pair. In two studies (Plant, Zumpe, Sauls & Michael, 1974; Robinson et al., 1975), each of which included 1 complete year, well-marked seasonal changes occurred in the plasma testosterone levels of male rhesus monkeys, with maxima in the autumn and winter months. A notable feature of our preliminary results was the occurrence of an autumnal increase although animals were maintained in a constant photoperiod. These studies have now been extended for a 3-year period during which environmental conditions were rigorously controlled to assess the extent to which long-term rhythms in plasma androgen levels are dependent on known exteroceptive factors.

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R. P. MICHAEL and E. B. KEVERNE

Many mammalian species breed seasonally and alterations in the physical environment provide the necessary stimulation. Zuckerman (1932) stated the case for the existence of an uninterrupted sexual life in monkeys and apes, but evidence has since accumulated that establishes breeding with annual rhythmicity in several primate species (Lancaster & Lee, 1965). In the rhesus monkey, a peak of births has been reported between March and May both in North India (Southwick, Beg & Siddiqi, 1961; Prakash, 1962; Lindburg, 1967) and also in the islands near Puerto Rico (Altmann, 1962; Koford, 1965). A survey of the breeding activity of rhesus monkeys in the laboratory shows different findings in different colonies (Ponce de Lugo, 1964), but there is considerable agreement that a similar birth peak occurs in captivity between March and April (Hartman, 1931; Rowell, 1963; Wisconsin data, 1966, quoted by Eckstein & Kelly, 1966). The existence of an annual (here we avoid the term 'seasonal') rhythm in sexual performance and motivation has been difficult to establish with certainty because of the annual disturbance caused by

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T. M. PLANT and R. P. MICHAEL

Summary.

Urinary excretion of androsterone was studied in four rhesus monkeys during six menstrual cycles. Androsterone excretion ranged from 28 to 388 μg/24 hr. In two menstrual cycles, the excretion of androsterone in the mid-luteal phase was approximately 60% greater than that in the follicular phase. In the remaining four cycles, enhanced excretion of androsterone in the luteal phase was not observed and therefore urinary androsterone does not appear to provide a reliable index of corpus luteum function in this macaque.

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RICHARD P. MICHAEL, D. ZUMPE, T. M. PLANT and R. G. EVANS

Department of Psychiatry, Emory University School of Medicine, Atlanta, Georgia 30322, and Georgia Mental Health Institute, Atlanta, Georgia 30306, U.S.A. (Received 10th February 1975)

Like many non-primate mammals, several non-human primates have wellmarked mating and birth seasons (Lancaster & Lee, 1965; Michael & Zumpe, 1971). In a relatively controlled laboratory environment, Michael & Keverne (1971) found that intact rhesus males paired with intact females, whose oviducts had been ligated to prevent pregnancy, showed a peak in ejaculatory activity in December followed by a decline between February and May. The timing of the long-term changes in potency of these laboratory males was, therefore, very similar to that occurring in the natural habitat in North India (Southwick et al., 1965; Michael & Wilson, 1975). This suggests the existence of an annual behavioural rhythm that is to some extent independent of major environmental variables. A clearcut annual rhythm in the plasma testosterone of

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R Michael Roberts, Kyle M Loh, Mitsuyoshi Amita, Andreia S Bernardo, Katsuyuki Adachi, Andrei P Alexenko, Danny J Schust, Laura C Schulz, Bhanu Prakash V L Telugu, Toshihiko Ezashi and Roger A Pedersen

It is imperative to unveil the full range of differentiated cell types into which human pluripotent stem cells (hPSCs) can develop. The need is twofold: it will delimit the therapeutic utility of these stem cells and is necessary to place their position accurately in the developmental hierarchy of lineage potential. Accumulated evidence suggested that hPSC could develop in vitro into an extraembryonic lineage (trophoblast (TB)) that is typically inaccessible to pluripotent embryonic cells during embryogenesis. However, whether these differentiated cells are truly authentic TB has been challenged. In this debate, we present a case for and a case against TB differentiation from hPSCs. By analogy to other differentiation systems, our debate is broadly applicable, as it articulates higher and more challenging standards for judging whether a given cell type has been genuinely produced from hPSC differentiation.

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Lucinda C Aulsebrook, Michael G Bertram, Jake M Martin, Anne E Aulsebrook, Tomas Brodin, Jonathan P Evans, Matthew D Hall, Moira K O’Bryan, Andrew J Pask, Charles R Tyler and Bob B M Wong

Environmental pollution is an increasing problem for wildlife globally. Animals are confronted with many different forms of pollution, including chemicals, light, noise, and heat, and these can disrupt critical biological processes such as reproduction. Impacts on reproductive processes can dramatically reduce the number and quality of offspring produced by exposed individuals, and this can have further repercussions on the ecology and evolution of affected populations. Here, we illustrate how environmental pollutants can affect various components of reproduction in wildlife, including direct impacts on reproductive physiology and development, consequences for gamete quality and function, as well as effects on sexual communication, sexual selection, and parental care. We follow with a discussion of the broader ecological and evolutionary consequences of these effects on reproduction and suggest future directions that may enable us to better understand and address the effects of environmental pollution.