Are precocial young cheaper? Lactation energetics in the guinea pig

Kunkele J, Trillmich F. Are precocial young cheaper? Lactation energetics in the guinea pig. PHYSIOLOGICAL ZOOLOGY. 1997;70(5):589-596.Caviomorphs stand out from other small rodents by producing extremely precocial young. Pups begin to nibble solid food right after birth and can survive weaning when 5 d old. We tested whether these properties of young lead to a low cost of lactation in guinea pigs (Cavia porcellus). In contrast to altricial rodents, energy acquisition and expenditure of guinea pig mothers (litter size, three) was highest during the first half of the 23-d lactation period. Daily metabolizable energy intake at peak lactation was increased by 126% above nonreproducing level and was 65% of the predicted maximal intake. peak daily energy expenditure was 1.9 times basal metabolic rate, and resting energy expenditure was elevated 26% above nonreproductive level. From the third day, young consumed solid food and intake increased linearly over the course of lactation. During lactation, total intake of litters through solid food consumption (assuming efficient digestion) amounted to 86% of the energy intake that mothers allocated to reproduction during that period. The pattern of energy expenditure during lactation in guinea pigs differs substantially from that of altricial rodents and is made possible because pups contribute through solid food intake. Overall energy demand on the mothers is not much lower than in altricial rodents, but lower peak energy demand during lactation in guinea pigs may reduce the coupling of reproduction to periods of high food abundance

Spacing behaviour and its implications for the mating system of a precocial small mammal: an almost asocial cavy Cavia magna?

Kraus C, Kunkele J, Trillmich F. Spacing behaviour and its implications for the mating system of a precocial small mammal: an almost asocial cavy Cavia magna? ANIMAL BEHAVIOUR. 2003;66(2):225-238.Socioecological models for small mammals attempt to explain the causal relations between the spatiotemporal distributions of food resources, females and males. We tested their predictions for a wild population of Cavia magna, a grazing, precocial rodent, by analysing spacing behaviour in relation to various demographic features. Between May 1999 and January 2001 we collected capture-recapture data on 309 individuals and monitored 55 females and 49 males by radiotelemetry in periodically inundated wetland in Uruguay. Cavies showed a nonstationary use of space: monthly home ranges drifted over the whole study site. Female home ranges overlapped with those of several others. Females were randomly distributed and we found no evidence for socially mediated reproductive synchrony. Males ranged over larger areas than females, showing even less site fidelity, and also overlapped with several rivals. This basic spacing system remained stable over a wide range of densities and sex ratios. Independent of sex, animals used overlap zones randomly with respect to each other. Significant dynamic (spatiotemporal) interaction was most frequent between males and females. However, interaction analyses revealed no evidence for stable social bonds between animals, regardless of sex. We suggest that unpredictable female locations prevent males monopolizing females spatially. Because females are solitary, males could monopolize only one female by maintaining close proximity, rendering a roaming mating tactic more successful. Our findings point to a solitary 'social' system and overlap promiscuity as the likely mating system for the C. magna population studied. (C) 2003 Published by Elsevier Ltd on behalf of The Association for the Study of Animal Behaviour

Reproduction and growth in a precocial small mammal, Cavia magna

Kraus C, Trillmich F, Kunkele J. Reproduction and growth in a precocial small mammal, Cavia magna. JOURNAL OF MAMMALOGY. 2005;86(4):763-772.Small mammals usually produce large litters of altricial young, resulting in high reproductive rates. In contrast, cavies give birth to few precocial young after a long gestation. The price of this reproductive strategy is a low intrinsic rate of natural increase. We investigated if the patterns of reproduction in a wild population of Cavia magna are consistent with the hypotheses that cavies can increase their reproductive output by breeding aseasonally and by maturing extremely early. We collected data on reproduction and growth by capture-recapture during a 26-month field study in a wetland in Uruguay, and from a laboratory population founded with individuals from the same region. Among the Caviinae, C. magna is particularly precocial, with individual neonates weighing on average 18% of maternal mass. Reproduction was mostly seasonal, with the main birth season starting at the end of September (austral spring) and extending until May in 1999 and February in 2000, respectively, with only a few females reproducing during the 1st but not the 2nd austral winter. Individual females produced on average 3 litters per year. Some females born in early spring conceived successfully between the age of 30 and 45 days, similar to females in the laboratory. The remainder of the 1st spring cohort and females of subsequent birth cohorts delayed reproduction until the following spring. Body condition and growth rates were highest in the spring, declined through the year, and varied between years, and may be the proximate factors deten-nining whether an adult female or a juvenile initiates breeding. Breeding opportunistically whenever conditions allow might partly compensate for the low reproductive rate of cavies

Does the unusual life history of the precocial cavy (Cavia magna) translate into an exceptional field metabolic rate?

Kunkele J, Kraus C, Trillmich F. Does the unusual life history of the precocial cavy (Cavia magna) translate into an exceptional field metabolic rate? PHYSIOLOGICAL AND BIOCHEMICAL ZOOLOGY. 2005;78(1):48-54.An association between metabolic rate and life history has been predicted but not demonstrated yet. To test this prediction, we measured the field metabolic rate (FMR) of a rodent, Cavia magna, which has an unusual combination of life-history traits. Cavies live aboveground, feed on energy-poor diets, and take relatively long to produce a few highly precocial young. This "slow-living" life history might predict a relatively low metabolic rate. We recorded FMR of 29 individuals of C. magna in Uruguay using doubly labeled water. This represents the first FMR record for a hystricomorph rodent. Besides body mass, season best explained variation in recorded FMR, with higher daily energy expenditures during winter. Surprisingly, the reproductive state of females did not affect FMR. Comparison with allometric prediction did not support the hypothesis that the slow-living life history of precocial grazing cavies translates into relatively low FMR. However, the clear effect of season on FMR as well as the fact that cavies appear able to compensate for the energy cost of reproduction might be associated with the nonburrowing precocial life history of this species

Living slow and dying young? Life-history strategy and age-specific survival rates in a precocial small mammal

Kraus C, Thomson DL, Kunkele J, Trillmich F. Living slow and dying young? Life-history strategy and age-specific survival rates in a precocial small mammal. JOURNAL OF ANIMAL ECOLOGY. 2005;74(1):171-180.1. Mammalian life histories can be ordered along a slow-fast continuum from slow-developing, long-lived species with low reproductive rates at one end to rapidly developing, short-lived species with high reproductive rates at the other. Body size and mortality rate are strong correlates of the slow-fast axis, whereby juvenile and adult mortality rates correlate positively but are linked to certain life-history traits with differing strengths. The strong covariation of life-history traits renders it difficult to evaluate the adaptive value of single life-history elements. Species that deviate from the common pattern might help to identify specific selected strategies. 2. Caviomorph rodents show an unusual combination of life-history traits. Like slow-living mammals, they produce few precocial young after long gestation periods, but they have the early maturation potential of their fast-living counterparts. This combination of life-history traits suggests low levels of juvenile mortality but high adult mortality rates, and thus an unusually low ratio of juvenile to adult mortality compared to other small mammals. To test these predictions, we modelled age-specific survival probabilities using capture-recapture data from a wild population of Cavia magna. 3. Patterns of age-specific survival rates were in accordance with the predictions, but atypical for small mammals. Levels of adult survival were low, and comparable to those of much smaller rodent species. Juvenile survival probabilities were high relative to those reported for other small mammals and reached adult levels after only 1 month. The ratio of adult to early juvenile survival depended strongly on the date of birth. Whereas survival of young from the first birth cohort in spring did not differ from that of adults, early survivorship of later cohorts was lower. 4. Our results fit expectations from life-history theory and suggest that high levels of adult mortality selected for the early onset of reproduction in wild cavies. The comparatively low juvenile mortalities are probably a consequence of the precocial state of the cavy offspring. We suggest that the reproductive strategy of cavies represents a different solution to the trade-off between fecundity and juvenile survival compared to altricial small mammals

Species-level differentiation of two cryptic species pairs of wild cavies, genera Cavia and Galea, with a discussion of the relationship between social systems and phylogeny in the Caviinae

Trillmich F, Kraus C, Kunkele J, et al. Species-level differentiation of two cryptic species pairs of wild cavies, genera Cavia and Galea, with a discussion of the relationship between social systems and phylogeny in the Caviinae. CANADIAN JOURNAL OF ZOOLOGY-REVUE CANADIENNE DE ZOOLOGIE. 2004;82(3):516-524.Two little-known species of guinea-pig from the genera Cavia and Galea (Cavia magna Ximenez, 1980 and Galea sp. nov.) have recently been studied in more detail with respect to their behavior, social structure, and mating system. To determine the specific distinctness of these little-known species from Cavia aperea Erxleben, 1777 and Galea musteloides Meyen, 1832, crossbreeding between species was tried and it demonstrated that the two Cavia species will rarely cross in captivity to produce hybrids of much reduced fertility, whereas the Galea species could not be crossed. To analyze the phylogenetic position of C. magna and Galea sp. nov., we present an analysis based on major parts of the 12S (778 base pair) and 16S genes of mitochondrial RNA (1435 base pair) in conjunction with corresponding data on all other genera of the Caviinae. We also determined the relationship between C. magna and the sympatric wild guinea-pig (C. aperea) and its domestic form (Cavia aperea f. porcellus (Linnaeus, 1758)). Phylogenetic and distance analysis of all genera of cavies (Cavia (two species), Galea (two species), Kerodon, Microcavia) showed the close relationship of C. magna with C. aperea and the latter's particularly low genetic distance to C. aperea f. porcellus. Galea sp. nov. differed markedly from G. musteloides. Of the three genera, Galea appears most distinct. The genus Kerodon clustered with the genus Hydrochaeris, supporting the previous conclusion by Rowe and Honeycutt (2002. Mol. Biol. Evol. 19: 263-277) regarding the placement of the genus Hydrochaeris within the Caviidae. Recently published data on the social systems of the above-mentioned cavy species, however, show their great inter- and intraspecific social flexibility and contradict the interpretation of the same authors about a simple relationship between phylogeny and social systems in the Caviidae

The preprotein translocation channel of the outer membrane of mitochondria

The preprotein translocase of the outer membrane of mitochondria (TOM complex) facilitates the recognition, insertion, and translocation of nuclear-encoded mitochondrial preproteins. We have purified the TOM complex from Neurospora crassa and analyzed its composition and functional properties. The TOM complex contains a cation-selective high-conductance channel. Upon reconstitution into liposomes, it mediates integration of proteins into and translocation across the lipid bilayer. TOM complex particles have a diameter of about 138 Angstrom, as revealed by electron microscopy and image analysis; they contain two or three centers of stain-filled openings, which we interpret as pores with an apparent diameter of about 20 Angstrom. We conclude that the structure reported here represents the protein-conducting channel of the mitochondrial outer membrane. [References: 75