Laboratory studies of the effect of temperature on growth, moulting and reproduction in the co-occurring mysids Neomysis integer and Praunus flexuosus

Abstract

The growth and reproduction of 2 co-occurring mysids (Neomysis integer Leach, 1814 and Praunus flexuosus F. Muller, 1776) were investigated against the background of their life cycle with individual-based experiments in the laboratory at 2 temperatures (10 and 15°C). The response of postmarsupial growth in relation to age in N. integer followed a sigmoid curve, based on an increase in both intermoult periods and growth factors. Maturity occurred after 15 to 16 moults and an age of 110 d at 10°C. At 15°C, the mean age was 45 d and mean length was 8 mm at maturity. Up to this stage they had moulted 9 to 10 times. In adults, growth rates decreased with increasing length. In post-larval and juvenile individuals of N. integer (3 to 7 mm), growth strongly depended on temperature as shown by high temperature coefficients (Q 10 = 4.0 to 7.4). The impact of temperature, on the growth of P. flexuosus was markedly different, the intermoult periods decreased while the growth factors increased with increasing temperature. At 15°C they needed 3.5 mo to mature and averaged 16 to 18 mm. P. flexuosus needed more than twice as long as N. integer to reach maturity, long enough for 2 generations of N. integer. In addition, temperature coefficients were markedly lower in juvenile P. flexuosus (Q 10 = 1.0 to 3.1) than in juvenile N. integer. The reproduction rate of N. integer was twice that of P. flexuosus. Incubation time for P. flexuosus was longer, fewer post-larval individuals emerged, and juveniles were 1 to 1.5 mm longer than juvenile N. integer. There were clear differences in the sequence of generations of N. integer and P. flexuosus, based on the development, time to maturity, number, and length of offspring. These interspecific differences in growth and reproduction enable a better insight into the life history strategies of N. integer and P. flexuosus and help to interpret the different distribution patterns, population structures, and the coexistence of these 2 species.