Effects of Temperature on Hatching Time and Hatchling Proportions in a Poecilogonous Population of Haminoea zelandiae

Abstract

Poecilogony is a relatively uncommon life-history strategy that results in the production of two different larval forms from the same egg mass (e.g., free-swimming lecithotrophic larvae and post-metamorphic, crawling juveniles). In this study, a population of the opisthobranch gastropod Haminoea zelandiae from Pauatahanui Inlet, New Zealand, was found to exhibit poecilogony. Further, differences in development, hatching times and proportion of hatchlings that were veligers or juveniles were examined for egg masses in two temperature regimes in the laboratory: cool (15-17 °C), and warm (21-23 °C). Hatching proportions were also examined for egg masses collected from the field (where temperatures ranged from 21-23 °C) for varying lengths of time (1 d, 5 d, and 10 d post-spawning). Hatchlings from egg masses in warmer temperatures developed faster and hatched earlier than those in cool temperatures. In the laboratory, egg masses in warm conditions hatched a greater proportion of post-metamorphic juveniles (45.4%) compared to egg masses in cool conditions (24.6%) Further, egg masses that had been in the field 10 d before hatching (i.e., more days at warmer temperatures) exhibited a greater proportion of post-metamorphic juveniles (67.9%) than those that were collected after only 1 d in the field (25.1%). Together these results suggest that temperature may have an important role in mediating dispersal strategies in this poecilogonous species.