1,721,189 research outputs found
Maternal investment and sex-allocation in the Galapagos fur seal, Arctocephalus galapagoensis
Full text linkTrillmich F. Maternal investment and sex-allocation in the Galapagos fur seal, Arctocephalus galapagoensis. Behavioral Ecology and Sociobiology. 1986;19(3):157-164.Maternal investment and sex-allocation were measured in a large, sexually dimorphic mammal, the Galapagos fur seal (Arctocephalus galapagoensis). The sex ratio at birth was 1.06. Males were always heavier than females and, at least initially, grew faster. Growth was variable from year to year suggesting energetic constraints on maternal investment. Sucking time conrrelated with milk intake. Mothers suckled yearling and 2-year-old sons more than daughters of the same age. Age at weaning appeared to be the same in both sexes or even slightly greater in males. No sex differences was found in mortality prior to weaning or in post-weaning dispersal. Birth rates of females with yearlings or 2-year-olds were significantly lower than those of females with no dependent young. Mothers invested more in sons than in daughters until weaning. It is unlikely that higher post-weaning investment in daughters balances the higher pre-weaning investment in sons. Data on sex ratio at birth, different growth rates, and weaning age of the sexes are typical of otariid seals as a group. The results of this study fit Maynard Smith's (1980) model of the evolution of sex allocation better than Fisher's (1930)
Ontogenetic changes in food intake and digestion rate of the herbivorous marine iguana (Amblyrhynchus cristatus, Bell)
Full text linkWikelski M, Gall B, Trillmich F. Ontogenetic changes in food intake and digestion rate of the herbivorous marine iguana (Amblyrhynchus cristatus, Bell). Oecologia. 1993;94(3):373-379
Female-female conflict in the harem of a snail cichlid (Lamprologus ocellatus): Behavioural interactions and fitness consequences
No full textBrandtmann G, Scandura M, Trillmich F. Female-female conflict in the harem of a snail cichlid (Lamprologus ocellatus): Behavioural interactions and fitness consequences. BEHAVIOUR. 1999;136(9):1123-1144.Female intra-sexual competition plays an important role in the settlement process during pair or harem formation and in established harems of Lamprologus ocellatus, a small snail shell inhabiting cichlid from Lake Tanganyika. Larger females settle first and this could partly be due to male preference for larger females as shown in simultaneous choice tests but is also due to dominance of the larger female. Smaller females were unable to settle close to a larger one. Even when snail shells were not limiting the smaller was either unable to settle or had to settle at a considerable distance. This effect was independent of prior residence. Intense female-female aggression suggests that close settlement is disadvantageous to females. Genetic analyses of maternity using microsatellite length polymorphism at five loci showed a reproductive skew between females in a harem. Additionally, it proved brood mixing in aquaria as well as in the field. Brood mixing can be detrimental to female breeding success through interbrood cannibalism if size difference of juveniles amounts to greater than or equal to 5 mm. Territoriality of juveniles, shown even between same-sized siblings, may cause indirect mortality through earlier dispersal of young. Females rejected experimentally added larger juveniles but accepted young smaller than their own fry. Acceptance of smaller juveniles could be advantageous through a dilution of predator attacks but it also appears to induce costs since females with young at the shell do not rear another brood. Large median distances of 91 cm maintained aggressively between breeding females in the field may serve to minimize the adverse effects of breeding in a harem
Vocal mother-offspring communication in guinea pigs: females adjust maternal responsiveness to litter size
Full text linkIn parent-offspring communication, vocal signals are often used to attract attention and offspring might call to induce parental behaviour. In guinea pigs (Cavia aperea f. porcellus) mothers wean larger litters later than small ones, but it is unknown whether this difference depends on processes induced during pregnancy or is influenced post-natally by the number of pups present. We here tested with playback-experiments using pup separation calls whether mothers with cross-fostered large experimental litters (four-pup-litters) were more responsive to offspring calls and maintained responsiveness for longer than mothers with small experimental litters (two-pup-litters). Mothers were tested when two pups were suckling i.e. when both teats were occupied. Results Mothers of four-pup litters responded stronger to broadcast pup separation calls than those with two-pup litters. Additionally, we tested the mothers' responsiveness to pup separation calls in the absence of their pups on day 8 and 20 of lactation. Mothers of four-pup litters responded stronger and showed no decrease in responsiveness from day 8 to 20, whereas mothers of two-pup litters responded less and decreased responsiveness from day 8 to 20. Mothers of four-pup litters also weaned their pu Conclusion Measured by their response to pup calls and by time to weaning, guinea pig mothers adjust maternal responsiveness to litter size. This behaviour is likely to be an adaptive strategy in resource allocation during reproduction.
Galápagos and Californian sea lions are separate species: genetic analysis of the genus Zalophus and its implications for conservation management
Full text linkWolf JBW, Tautz D, Trillmich F. Galápagos and Californian sea lions are separate species: genetic analysis of the genus Zalophus and its implications for conservation management. Frontiers in Zoology. 2007;4(1): 20.Background: Accurate formal taxonomic designations are thought to be of critical importance for the conservation of endangered taxa. The Galápagos sea lion (GSL), being appreciated as a key element of the Galápagos marine ecosystem, has lately been listed as 'vulnerable' by the IUCN. To date there is, however, hardly any scientific evidence, whether it constitutes a separate entity from its abundant Californian neighbour (CSL). In this paper, we delineate the taxonomic relationships within the genus Zalophus being comprised of the Galápagos sea lion, the Californian sea lion and the already extinct Japanese sea lion (JSL). Results: Using a set of different phylogenetic reconstruction approaches, we find support for monophyly of all three taxa without evidence of reticulation events. Molecular clock estimates place time to common ancestry of the Galápagos sea lion and the Californian sea lion at about 2.3 ± 0.5 mya. Genetic separation is further suggested by diagnostic SNPs in the mitochondrial and nuclear genome. Microsatellite markers confirm this trend, showing numerous private alleles at most of the 25 investigated loci. Microsatellite-based estimates of genetic differentiation between the Galápagos sea lion and the Californian sea lion indicate significant genetic differentiation. Gene diversity is 14% lower in the Galápagos sea lion than in the Californian sea lion, but there is no evidence for recent bottleneck events in the Galápagos sea lion. Conclusion: Based on molecular evidence we build a case for classifying the Galápagos sea lion (Zalophus wollebaeki), the Californian sea lion (Zalophus californianus) and the Japanese sea lion (Zalophus japonicus) as true species. As morphological characters do not necessarily fully reflect the rapid divergence on the molecular level, the study can be considered as a test case for deriving species status from molecular evidence. We further use the results to discuss the role of genetics in conservation policy for an organism that already is under the general protection of the habitat it lives in
Tracing early stages of species differentiation: Ecological, morphological and genetic divergence of Galapagos sea lion populations
Full text linkBackground: Oceans are high gene flow environments that are traditionally believed to hamper the build-up of genetic divergence. Despite this, divergence appears to occur occasionally at surprisingly small scales. The Galápagos archipelago provides an ideal opportunity to examine the evolutionary processes of local divergence in an isolated marine environment. Galápagos sea lions (Zalophus wollebaeki) are top predators in this unique setting and have an essentially unlimited dispersal capacity across the entire species range. In theory, this should oppose any genetic differentiation. Results: We find significant ecological, morphological and genetic divergence between the western colonies and colonies from the central region of the archipelago that are exposed to different ecological conditions. Stable isotope analyses indicate that western animals use different food sources than those from the central area. This is likely due to niche partitioning with the second Galápagos eared seal species, the Galápagos fur seal (Arctocephalus galapagoensis) that exclusively dwells in the west. Stable isotope patterns correlate with significant differences in foraging-related skull morphology. Analyses of mitochondrial sequences as well as microsatellites reveal signs of initial genetic differentiation. Conclusion: Our results suggest a key role of intra- as well as inter-specific niche segregation in the evolution of genetic structure among populations of a highly mobile species under conditions of free movement. Given the monophyletic arrival of the sea lions on the archipelago, our study challenges the view that geographical barriers are strictly needed for the build-up of genetic divergence. The study further raises the interesting prospect that in social, colonially breeding mammals additional forces, such as social structure or feeding traditions, might bear on the genetic partitioning of populations
The behavioral ecology of maternal effort in fur seals and sea lions
Full text linkTrillmich F. The behavioral ecology of maternal effort in fur seals and sea lions. Behaviour. 1990;114(1):3-20
Temperature regulation and microhabitat choice by free-ranging Galapagos fur seal pups (Arctocephalus galapagoensis)
Full text linkLimberger D, Trillmich F, Biebach H, Stevenson RD. Temperature regulation and microhabitat choice by free-ranging Galapagos fur seal pups (Arctocephalus galapagoensis). Oecologia. 1986;69(1):53-59
Characterization of proteins and fatty acid composition in galapagos fur seal milk. Occurrence of whey and casein protein polymorphisms
Full text linkTrillmich F, Kirchmeier D, Kirchmeier O, et al. Characterization of proteins and fatty acid composition in galapagos fur seal milk. Occurrence of whey and casein protein polymorphisms. Comparative Biochemistry and Physiology, Part B: Biochemistry and Molecular Biology. 1988;90(2):447-452
Mama's boy: sex differences in juvenile survival in a highly dimorphic large mammal, the Galapagos sea lion
No full textKraus C, Mueller B, Meise K, Piedrahita P, Pörschmann U, Trillmich F. Mama's boy: sex differences in juvenile survival in a highly dimorphic large mammal, the Galapagos sea lion. Oecologia. 2013;171(4):893-903.In many mammals, early survival differs between the sexes, with males proving the more fragile sex ["Fragile male (FM) hypothesis"], especially in sexually dimorphic species where males are the larger sex. Male-biased allocation (MBA) by females may offset this difference. Here, we evaluate support for the FM and MBA hypotheses using a dataset on Galapagos sea lions (Zalophus wollebaeki). We statistically model sex-specific survival as it depends on body mass and environmental conditions (sea surface temperature, SST, a correlate of marine productivity) at three developmental stages, the perinatal phase (1st month), the main lactation period (1st year), and the weaning period (2nd year). Supporting the FM hypothesis, we found that, early in life (1st month), at equal birth mass, males survived less well than females. During the remainder of the first year of life, male survival was actually less sensitive to harsh environmental conditions than that of females, contradicting the FM hypothesis and supporting the MBA hypothesis. During the second year of life, only male survival suffered with high SSTs as predicted by the FM hypothesis. At each developmental stage, observed survival rates were almost equal for both sexes, suggesting that mothers buffer against the inherent fragility of male offspring through increased allocation, thereby masking the differences in survival prospects between the sexes
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