Distinct longevity mechanisms across and within species and their association with aging

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A test of alternative hypotheses for kin recognition in cannibalistic tiger salamanders

The function of kin recognition is controversial. We investigatedthe adaptive significance of kin discrimination in cannibalistictiger salamander larvae, Ambystoma tigrinum. Previous laboratoryexperiments show that cannibals preferentially consume lessrelated individuals. We hypothesized that this example of kinrecognition (1) is a laboratory artifact, (2) is a by-productof sibship-specific variation in escape responses, because cannibalsfrom families with rapid responses may be more likely to cannibalize slowlyescaping non-kin, (3) is an epiphenomenon of species recognition,(4) functions in disease avoidance, because kin may be moreinfectious than non-kin, or (5) is favored by kin selection.We evaluated these five hypotheses by using laboratory and fieldexperiments to test specific predictions made by each hypothesis.We rejected hypotheses 1-4 above because (1) kin recognitionwas expressed in the wild, (2) escape responses did not reliablypredict whether a cannibal would ingest kin or non-kin, (3)kin recognition was not most pronounced in populations wheretiger salamanders co-occur with other species of salamanders,and (4) non-kin prey were more likely than kin to transmit pathogensto cannibals. However, we established that the necessary conditionfor kin selection, Hamilton's rule, was met. Thus, our resultsimplicate kin selection as the overriding reason that cannibalistictiger salamanders discriminate kin.     

The myoglobin of rodents:Lagostomus maximus (viscacha) andSpalax ehrenbergi (mole rat)

The primary sequences of the myoglobins of two rodents (the South American viscacha and the Mediterranean mole rat) have been determined. Both myoglobins exhibit one polymorphism. The two rodent sequences have been compared with each other and with other known myoglobins. The myoglobin of the viscacha is similar to those of the diving mammals and penguin in having a high arginine content. Among mammalian sequences, the arginines at positions 77 (in one of the viscacha myoglobins) and 79 have been found only in the myoglobin from viscacha. Mole rat myoglobin has a lysine at position 31, where arginine or serine is found in all other known vertebrate myoglobins.     

Intercolonial encounters and xenophobia in the common mole rat, Cryptomys hottentotus hottentotus (Bathyergidae): the effects of aridity, sex, and reproductive status

The ecological constraints prevalent in arid environments havepromoted the evolution of social groups with a high reproductiveskew in mole rat species occurring there. Outbred social bathyergidsface conflict between maintaining colony integrity to enhancepersonal foraging success and hence survival, and dispersalto maximum individual lifetime reproductive success (LRS). Thisconflict will be a crucial determinant of the response of colonymembers to the presence of foreign conspecifics. We investigatedhow ecological constraints, sex, and reproductive status influencethe outcome of meetings between foreign common mole rats (Cryptomyshottentotus hottentotus) in a series of dyadic encounters. Individualsfrom two localities, at the extremes of an aridity gradient,were used to assess the effects of aridity. The effects of sexand reproductive status were investigated by trials betweenindividuals of differing sex and status. The arid populationrevealed substantially higher levels of rejection than the mesicpopulation. Sex and status played a significant role in moderatingindividual response. For both populations, encounters betweendifferent-sexed individuals produced lower levels of rejectionthan those between same-sexed individuals. For the mesic site,rejection was greatest for encounters between reproductive animals.Conversely, for the arid site, the levels of rejection werecomparatively high and comparable for all combinations of reproductivestatus. Ecological constraints, sex, and reproductive statusare significant factors in interactions between foreign commonmole rats, ultimately influencing individual survival, colonyintegrity and the differential LRS of all colony members. Ourresults provide insight into the evolution and maintenance offamily groups within the bathyergids.     

Pathogenicity of Steinernema scapterisci to Selected Invertebrates

Steinernema scapterisci was more pathogenic to insects tested in the order Orthoptera than to those in the orders Lepidoptera or Hymenoptera; it was not pathogenic to earthworms. The nematode also infected and killed the mole crickets Scapteriscus acletus and S. vicinus when released four successive times at 10-day intervals in containers of soil infested with the nematode.