Horses, asses, and zebras belong to a single genus, Equus, which emerged 4.0-4.5 Mya. Although the equine fossil record represents a textbook example of evolution, the succession of events that gave rise to the diversity of species existing today remains unclear. Here we present six genomes from each living species of asses and zebras. This completes the set of genomes available for all extant species in the genus, which was hitherto represented only by the horse and the domestic donkey. In addition, we used a museum specimen to characterize the genome of the quagga zebra, which was driven to extinction in the early 1900s. We scan the genomes for lineage-specific adaptations and identify 48 genes that have evolved under positive selection and are involved in olfaction, immune response, development, locomotion, and behavior. Our extensive genome dataset reveals a highly dynamic demographic history with synchronous expansions and collapses on different continents during the last 400 ky after major climatic events. We show that the earliest speciation occurred with gene flow in Northern America, and that the ancestor of present-day asses and zebras dispersed into the Old World 2.1-3.4 Mya. Strikingly, we also find evidence for gene flow involving three contemporary equine species despite chromosomal numbers varying from 16 pairs to 31 pairs. These findings challenge the claim that the accumulation of chromosomal rearrangements drive complete reproductive isolation, and promote equids as a fundamental model for understanding the interplay between chromosomal structure, gene flow, and, ultimately, speciation.equids | evolutionary genomics | speciation | admixture | chromosomal rearrangements

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Reproduction of African elephants Loxodonta africana and Asian elephants Elephas maximus has in the past been poor in European zoos and juvenile survival has been low. A range of potential complications, such as stillbirths or maternal aggression towards the calf, makes it imperative that the date of parturition is predicted as accurately as possible. Behavioural, endocrinological and physiological data were collected from three pregnant elephants for up to 3 months prior to parturition in order to assess their value for predicting the date of birth. Behavioural observations indicated that activity, particularly the frequency of stereotypic behaviour, increased prior to parturition. Pregnant cows grew restless and exhibited frequent excretion, tail beating against the vulva and excessive throwing of hay or sand against the belly. Our results suggest that observations of prepartal behavioural changes are a useful indicator for predicting parturition, particularly for veterinarians and keepers who are familiar with the usual behaviour patterns of the animals in their care. Measurement of luteal activity indicated that luteo‐lysis occurred 2‐3 days prior to parturition in both elephant species. Thus, endocrinological analysis provides an excellent and accurate prediction of the timing of parturition.

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The corpus luteum of African elephants produces high amounts of 5α‐reduced progesterone metabolites (5α‐pregnane‐3,20‐dione and 5‐α‐pregnane‐3α‐ol‐20‐one), whereas progesterone itself is quantitatively less important, and plasma levels of progesterone during the estrous cycle in elephants are considerably lower than those of other mammals. The objective of this study was to compare the concentration of progesterone in plasma of Asian and African elephants as determined by specific progesterone assays with those of total immunoreactive progestagens containing a 20‐oxo‐group (20‐oxo‐P). These metabolites were determined by an enzyme immunoassay using an antibody against 5‐α‐pregnane‐3β‐ol‐20‐one, 3HS:BSA. Plasma of non‐pregnant Asian (n = 4) and African (n = 4) elephants was collected at weekly intervals for periods of 8–15 months and at random intervals during pregnancy in one Asian elephant. High‐performance liquid chromatography separation of plasma samples of both species demonstrated that in the 20‐oxo‐P assay, 5α‐pregnane‐3,20‐dione makes up ˜60% of the total immunoreactive material. The progesterone and 20‐oxo‐P values during the estrous cycle showed a parallel pattern and were significantly correlated (P < 0.001; Asian: r = 0.80; y = 3.76 × –0.10; African: r = 0.75; y = 2.66 × –0.08). Progesterone and 20‐oxo‐P values in Asian and African elephants were <0.15 ng/ml during the follicular phase (weeks –4 to 0) of the estrous cycle; progesterone values during the luteal phase (weeks 2–9) were 0.60 ± 0.03 and 0.53 ± 0.03 ng/ml, and the 20‐oxo‐P values were 2.19 ± 0.16 and 1.48 ± 0.12 ng/ml, respectively. The 20‐oxo‐P values of the pregnant animal, although slightly higher, were comparable to those of non‐pregnant elephants during the luteal phase. Total immunoreactive 20‐oxo‐P values are about three times higher than those of progesterone during the luteal phase, and 5α‐pregnane‐3,20‐dione is the major immunoreactive 20‐oxo‐P in the plasma of Asian and African elephants. Zoo Biol 16:403–413, 1997. © 1997 Wiley‐Liss, Inc.