REPRODUCTION IN FEMALE WILD GUINEA-PIGS J. P. ROOD and BARBARA J. WEIR Department ofZoology, MichiganState University, East Lansing, Michigan, U.S.A. and Wellcome Institute of Comparative Physiology, Zoological Society of London, Regent's Park, London, jV. W. 1 (Received 10th December 1969) Summary. The breeding characteristics of three species of wild guinea- pig (F. Caviidae) are reported. Cavia aperea, Galea musteloides and Micro- cavia australis were studied in Argentina in the field and in outdoor pens, and laboratory colonies of the two former species were also established in England. Pens of domestic guinea-pigs (Cavia porcellus) and of C. aperea \m=x\C. porcellus hybrids were maintained in Argentina for comparisons with C. aperea. C. aperea and G. musteloides gave birth in every month but there was a breeding peak in spring (September to December). Microcavia had a more restricted breeding season ; in the field study area, births occurred only between August and April. Gestation length in C. aperea was variable but the mode was at 61 days, while the modes of Galea and Microcavia were much shorter at 53 and 54 days, respectively. All three species exhibited a post-partum oestrus and Galea may experience a lactation anoestrus. Oestrous cycle lengths in C. aperea and Galea varied consider- ably but the mean length in Cavia was 20\m=.\6\m=+-\0\m=.\8days and in Galea it was 22\m=.\3\m=+-\1 \m=.\4days; in the latter species, the presence of a male in the same cage was necessary for the induction of oestrus. Average litter size was 2\m=.\2for C. aperea, 2\m=.\6for Galea and 2\m=.\8for Microcavia. In the Argentine colonies, the age at first conception in C. aperea and Galea varied with the time of year of birth, but this variation was not maintained under the more equable laboratory conditions. INTRODUCTION Although the domestic guinea-pig, Cavia porcellus, has been kept in captivity for over 400 years, little information has been published on wild guinea-pigs. Those studies which have been reported have mainly been concerned with the taxonomy and distribution of cavies (Cabrera, 1954) and with the genetics of the genus Cavia (Detlefson, 1914; Castle & Wright, 1916; Ubisch & Mello, 1940). These authors give some data on reproduction in the species which they studied and Pearson (1951) gives a little information on Galea musteloides in Peru. Nothing else appears to have been published on the reproductive biology of any wild members of this family (Caviidae) of hystricomorph rodents. The * Enquiries concerning reprints should be addressed to Dr . J. Weir. 393 Downloaded from Bioscientifica.com at 10/10/2021 10:51:38AM via free access 394 J. P. Rood and Barbara J. Weir literature on reproduction of the domestic guinea-pig is, of course, extensive (see Asdell, 1964; Marshall, 1952-66). Various other hystricomorphs have been studied, mainly in captivity, and several unusual features of their reproductive physiology have been reported (Weir, 1967a). All except the coypu (Myocastor coypus) have a vaginal closure membrane which is perforate at oestrus and parturition. Apart from the sub-family Caviinae, all other hystricomorphs investigated have very long pregnancies ofover 100 days and this is not associated with a delay ofimplanta¬ tion such as is found in various other species (e.g. roe deer, stoat, bear, badger, armadillo). The oestrous cycle is also longer in other hystricomorphs than the 16^-day cycle of the domestic guinea-pig. For example, both the chinchilla (Chinchilla laniger) and the plains viscacha (Lagostomus maximus) have a mean cycle length of 41 days (Weir, 1966; Weir, in preparation) and the cycle length in the dasyproctids (Dasyprocta and Myoprocta) is about 35 days (Weir, 1967b; Kleiman, 1969). During the course of investigations into the comparative behaviour of wild guinea-pigs in Argentina (Rood, in preparation), information was obtained on the breeding characteristics of three species of different genera. Colonies of two of these species were also established in London and the breeding data compiled at both places are compared below. The species identifications for Galea musteloides (PI. 1, Fig. 2) and Microcavia australis (PI. 1, Fig. 1) are based on Cabrera (1954); but for Cavia aperea (PL 1, Fig. 3) the recommendation of Hiickinghaus (1962) has been followed. MATERIALS AND METHODS Observations in Argentina (December 1965 to February 1968) The three wild species (Cavia aperea, Galea musteloides and Microcavia australis) were observed in the areas shown in Text-fig. 1 and limited trapping and observations were also made in several other localities. Colonies of each of these three species, and of the domestic guinea-pig (Cavia porcellus) and of C. apereaxC. porcellus hybrids were maintained in large pens at Sierra de la Ventana, Buenos Aires Province. Cavies were trapped live in the study areas by mesh, treadle-type traps (National Live Traps) placed in their runways. Each animal was individually marked by toe clipping and with Nyanzol dye. Total length and weight were recorded and compared with data on animals of the field and pen populations of known age in order to assess approximate ages. Pregnancy was determined by palpation. The pens were initially stocked with Galea and C. aperea trapped within a 40-km radius of Sierra de la Ventana; the Microcavia colony was established with animals brought from the study area in southern Buenos Aires Province. The original C. porcellus stock was donated and the hybrids were obtained by crossing female C. porcellus with a C. aperea male caught in the wild. The colonies were allowed to grow naturally until about twenty-five animals were present and were then controlled by removing newly weaned animals. Such removals were only necessary for the Galea population as, although all the species did Downloaded from Bioscientifica.com at 10/10/2021 10:51:38AM via free access PLATE 1 Fig. 1. Microcavia australis ( 0-5). Fig. 2. Galea musteloides ( 0-5). Fig. 3. Cavia aperea ( 0-3). (Facing p. 394) Downloaded from Bioscientifica.com at 10/10/2021 10:51:38AM via free access Reproduction infernale wild guinea-pigs 395 breed in the pens, the reproductive success varied considerably and was highest in Galea and lowest in Microcavia. The wire mesh pens were each 5 5 2 m high ; the mesh was extended 75 cm underground to prevent escape but only the Microcavia were found to burrow. The principal shelter in each pen consisted of four waterproof nest boxes which were kept supplied with fresh sawdust. Additional shelter was provided by an inverted metal tub in the Microcavia pen and open wooden boxes in the other pens. All the pens were supplied with branches for climbing. Commercial rabbit Text-fig. 1. Map of part ofArgentina to show the areas ofstudy and the sources of cavies investigated in captivity: (1) Cavia aperea study area; 'Estancia El Destino', 20 km S.E. Magdalena. (2) Microcavia australis study area; 'Estancia La Cristina', 14 km S.E. Cardenal Cagherò. (3) Galea musteloides study area ; 'Estancia La Sorpresa', 5 km E. Torn- quist, and source of G. Musteloides for London colony. A, Source of C. aperea for London colony. ·, All three species in the penned colonies, Sierra de la Ventana. pellets (Purina), whole oats and water were always available; a selection of grasses, carrots, lettuce, apples and potatoes was given once a day. Lawn grass was grown under wire mesh frames to supplement the supply of green food. Observations in London (August 1967 to August 1969) The C. aperea and G. musteloides colonies were derived from three C. aperea (one male, two females) caught in the wild and from ten Galea (four males, six Downloaded from Bioscientifica.com at 10/10/2021 10:51:38AM via free access 396 J. P. Rood and Barbara J. Weir females) which were either from the pen colonies (see above) or had been trapped immediately before their transfer to London. Both species were initially kept in small groups in standard guinea-pig cages, but C. aperea is now housed in floor pens and Galea in mesh cages with solid floors. Details of the housing and husbandry are given by Weir (1970). The animals were checked daily for reproductive condition and all events, such as vaginal opening, copulatory plugs and litters, were recorded. Oestrous cycle length was defined as the interval from the 1st day ofvaginal opening ofone cycle up to, but not including, the 1st day of opening at the next cycle. The day of finding a copulatory plug was recorded as Day 1 of pregnancy; most gestation lengths were, however, determined from the interval between births of litters as there is an immediate post-partum oestrus in these species. Standard statistical tests were applied and mean values are followed by the standard error of the mean. RESULTS A. CAVIA SPP. 1. Annual reproductive cycle Under laboratory conditions, domestic guinea-pigs breed throughout the year, although slight seasonal variations in reproductive performance have been reported (Rowlands, 1949; Wright, 1960). Castle & Wright (1916) reported that their colony of Cavia cutleri, obtained from Peru and maintained in the United States, bred in all months, but thirty-eight litters were born from January to June as against fifteen born from June to January. It is clear from Text-fig. 2 that, in Argentina (B, C and D), Cavia species breed throughout the year, although there is an indication that reproductive activity is reduced in C. aperea (B) during the autumn and winter months (April to August). In the combined data for the 2-year period studied, 42% to 87% of C. aperea females over 3 months old were pregnant in each month from August to February whereas only 9% to 25% were pregnant from March to July.