Reproductive strategy of a cave-living arachnid with indeterminate growth (Phrynus longipes; Amblypygi: Phrynidae)

Abstract

Natural selection predicts that organisms should maximize reproductive fitness by exhibiting a tradeoff between the quantity and quality of offspring. While many species clearly show this tradeoff, it is not a ubiquitous phenomenon. Indeed, observing this tradeoff in different organisms is contingent on life history traits, reproductive strategy, parental investment, and physiological constraints. We tested for a tradeoff between the number and quality of offspring in the amblypygid Phrynus longipes (Pocock, 1894)—a long-lived, iteroparous arachnid with indeterminate growth, post-ultimate molts, and parental care. We measured the size of gravid females and the mass and number of eggs in their clutches. Egg count, but not mass, was predicted by female size, indicating that we did not detect an offspring quantity-quality tradeoff. We posit that larger female P. longipes are laying more eggs rather than increasing investment in each egg. This study is the first of its kind in any amblypygid species.