Physical and Cognitive Performance of the Least Shrew (Cryptotis parva) on a Calcium-Restricted Diet.

Jessica L Czajka,Danielle E Garneau,Timothy S Mccay

doi:10.3390/bs2030172

Abstract

Geological substrates and air pollution affect the availability of calcium to mammals in many habitats, including the Adirondack Mountain Region (Adirondacks) of the United States. Mammalian insectivores, such as shrews, may be particularly restricted in environments with low calcium. We examined the consequences of calcium restriction on the least shrew (Cryptotis parva) in the laboratory. We maintained one group of shrews (5 F, 5 M) on a mealworm diet with a calcium concentration comparable to beetle larvae collected in the Adirondacks (1.1 ± 0.3 mg/g) and another group (5 F, 3 M) on a mealworm diet with a calcium concentration almost 20 times higher (19.5 ± 5.1 mg/g). Animals were given no access to mineral sources of calcium, such as snail shell or bone. We measured running speed and performance in a complex maze over 10 weeks. Shrews on the high-calcium diet made fewer errors in the maze than shrews on the low-calcium diet (F1,14 = 12.8, p < 0.01). Females made fewer errors than males (F1,14 = 10.6, p < 0.01). Running speeds did not markedly vary between diet groups or sexes, though there was a trend toward faster running by shrews on the high calcium diet (p = 0.087). Shrews in calcium-poor habitats with low availability of mineral sources of calcium may have greater difficulty with cognitive tasks such as navigation and recovery of food hoards.

Highlights

Chronic acidic deposition, which results from air pollution, increases environmental exposure to toxins and depletes important nutrient cations, including calcium [1,2]
Calcium content of invertebrates in forests with calcium-rich soils is greater than invertebrates found associated with calcium-poor soils [9]
We studied the physical and cognitive performance of least shrews maintained on diets that differed in calcium availability

Summary

Introduction

Chronic acidic deposition, which results from air pollution, increases environmental exposure to toxins and depletes important nutrient cations, including calcium [1,2]. Habitats affected by acidic deposition often have low or reduced abundance of high-calcium invertebrate animals, including snails [3,4,5,6]. Snail shells are an important source of calcium for passerines and reduced snail density may result in increased eggshell deformities and population declines [4,7]. Tree swallows (Tachycineta bicolor) experience reduced fitness and altered foraging behavior in areas with low calcium, resulting in longer search times and greater predation risk [8]. Perhaps to compensate for lower calcium availability in invertebrates, passerine birds consume more oak (Quercus spp.) buds in areas with low soil calcium. The need to supplement diets with hardwood buds, in areas depleted of calcium, might interestingly exacerbate losses attributed to white-tailed deer (Odocoileus virginianus) browsing in northern forests [10,11]

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