Seasonal shifts in the life cycle of the ponto-caspian invader Limnomysis benedeni (Crustacea: Mysida): a physiological adaptation?

Abstract

The mysid Limnomysis benedeni, one of the most important ponto-caspian invaders, was found in Lake Constance (southern Germany) in 2006. As part of larger studies to evaluate the effects of L. benedeni on the ecosystem, we studied its life-cycle strategies over an entire seasonal cycle in intervals of 3-5 weeks, addressing factors (predation, temperature) which we expected to be most important triggers of the observed changes. The size class distribution and the reproductive pattern indicated that the life cycle of L. benedeni changes seasonally. During winter (November to March), the mysid invested energy in growth and delayed reproduction until April, when the population was dominated by adults. In summer (June to September), the adults reproduced at a smaller body size and the population was disproportionately dominated by juveniles. In a mesocosm experiment that excluded fish predators, the mysids followed the same seasonal patterns of growth and energy investment as in the field population, but the size class distribution differed. Even in summer, the population in the mesocosm was dominated by adults. Stomach analyses of fish showed that L. benedeni is preyed upon by juvenile Perca fluviatilis, which fed size selectively on larger mysids. In conclusion, our results suggest predation was the reason for the dominance of juveniles and the observed size class distribution in summer. In contrast, the smaller adults in summer were most likely a physiological adaptation, perhaps evolved to avoid predation or as a reaction on metabolic losses at higher temperatures.

Embryonic development time of the freshwater mysid Limnomysis benedeni Czerniavsky as a function of water temperature

“…At 4°C, eggs did not develop. The coldest temperature at which the larvae developed to juveniles was at 6.5°C, which is close to the temperature measured in the field at which the first breeding females were found in spring 2008 (6.6°C, Hanselmann et al 2011). Because of the negative exponential relationship, fluctuations at lower temperatures cause much higher changes in the development time than fluctuations at higher temperatures.…”

“…The tested temperatures between 4 Aquat Ecol (2011) 45:539-546 541 and 25°C represent the range observed in the littoral of Lake Constance (Stich and Brinker 2010;Hanselmann et al 2011) and in most lakes in temperate zones in which L. benedeni is found (Wittmann and Ariani 2008;Audzijonyte et al 2009). At 4°C, eggs did not develop.…”

“…L. benedeni is well adapted to the temporal conditions in Lake Constance, as indicated by the maximal survival of larvae and adults at 15.9°C. The mean temperature in the field during the reproduction period in 2008 was 15.6 ± 5.7°C, with a minimum of 6.6°C at the beginning on April 2 and a maximum of 22.9°C in midsummer on July 30 (Hanselmann et al 2011). This could also explain the rapid increase in L. benedeni after its introduction in Lake Constance (Hanselmann, unpublished observations).…”

“…At the end of July, when we started the experiment, only few breeding females were found. At this time, the abundance of the population of L. benedeni in Lake Constance was lower probably because of size-selective predation by juvenile perch on the large-length classes of the mysid (Hanselmann et al 2011). Because of reduced adults available in the field, it could be that in our sampling no female was included with a clutch fertilized the night before.…”

“…In spring, the large overwintering females produce large egg clutches. In summer, adults reach maturity at a size smaller than that in winter and produce smaller clutches (Hanselmann et al 2011).…”