A multifactor investigation of the reproductive fitness responses of the land snail Neohelix (=Triodopsis) albolabris to levels of temperature, humidity, nutrition, calcium, and parasitism, by the nematode Parelaphostrongylus tenuis
Abstract
Ecosystems are collections of abiotic and biotic factors, hierarchically arrayed, and inclined toward interaction. The actions and interactions of ecological factors are fundamental in the determination of individual fitnesses and thus the selection pressures for the evolution of life histories for an ecosystem's organisms. Confronted with the multifactor structure of an ecosystem, a multifactor experimental design would thus seem requisite for the elucidation of the mechanisms of an ecosystem. Experimental multifactor environments of five factors (parasite burden, temperature, humidity, nutrition, and calcium) at three levels were used to produce life history data in an investigation of the extant reproductive fitness variations for the land snail Neohelix (= Triodopsis) albolabris. First through third stage larvae (L$\sb1$-L$\sb3$) of Parelaphostrongylus tenuis (Nematoda: Metastrongyloidea) commonly infect N. albolabris in its natural habitat and were used for the parasite burden in the present study. Life history responses of the snails to the levels of environmental factors indicated significant variation in the number and quality of their eggs and offspring. Additionally, levels of abiotic factors within the environment of the host influenced the rate of nematode development, and thus the magnitude of the infective parasitic populations. Two life history patterns were observed corresponding to the relative amount of environmental stress. Environments favoring increases in adult snail activity, egg and hatchling energy, and hatchling growth rates contained low levels of environmental stress. Factor combinations benefiting environmental tolerance allowed snails to accrue energy from foraging and to channel energy into life history functions. Parasitic populations competed for nutrient-derived snail energy, and their effects were somewhat offset by favorable host environmental tolerance and nutritional levels. Larval development rates were enhanced by low temperature and high nutrition host environments. Stressful conditions for the experimental snails occurred within environments reducing the acquisition of nutrition and thus energy for life history functions. In stressful environments snail reproductive effort was characterized by delayed oviposition of large clutches with high hatching success, but also high hatchling mortality and lower hatchling growth rates. The higher mortality and lower early growth rates infer limited energy resources partitioned from stressed adults into their eggs.
Subject Area
Ecology
Recommended Citation
Maze, Robert Joseph, "A multifactor investigation of the reproductive fitness responses of the land snail Neohelix (=Triodopsis) albolabris to levels of temperature, humidity, nutrition, calcium, and parasitism, by the nematode Parelaphostrongylus tenuis" (1993). Dissertations available from ProQuest. AAI9321440.
https://repository.upenn.edu/dissertations/AAI9321440