Differences in Time until Dispersal between Cryptic Species of a Marine Nematode Species Complex

Abstract

Co-occurrence of closely related species may be achieved in environments with fluctuating dynamics, where competitively inferior species can avoid competition through dispersal. Here we present an experiment in which we compared active dispersal abilities (time until first dispersal, number and gender of dispersive adults, and nematode densities at time of dispersal) in Litoditis marina, a common bacterivorous nematode species complex comprising four often co-occurring cryptic species, Pm I, II, III, and IV, as a function of salinity and food distribution. The experiment was conducted in microcosms consisting of an inoculation plate, connection tube, and dispersal plate. Results show species-specific dispersal abilities with Pm I dispersing almost one week later than Pm III. The number of dispersive adults at time of first dispersal was species-specific, with one dispersive female in Pm I and Pm III and a higher, gender-balanced, number in Pm II and Pm IV. Food distribution affected dispersal: in absence of food in the inoculation plate, all species dispersed after ca four days. When food was available Pm I dispersed later, and at the same time and densities irrespective of food conditions in the dispersal plate (food vs no food), suggesting density-dependent dispersal. Pm III dispersed faster and at a lower population density. Salinity affected dispersal, with slower dispersal at higher salinity. These results suggest that active dispersal in Litoditis marina is common, density-dependent, and with species, gender- and environment-specific dispersal abilities. These differences can lead to differential responses under suboptimal conditions and may help to explain temporary coexistence at local scales.

Cryptic diversity and ecosystem functioning: a complex tale of differential effects on decomposition

“…It is, therefore, surprising that Pm III did not differ more from Pm I and Pm IV in its effect on enzymatic activity in this experiment. The two genetically most closely related species (Pm I and Pm IV) do not show big differences in ecological characteristics (De Meester et al 2012, 2015b; however, in the present study, Pm IV always showed a more positive effect on the β-glucosidase activity compared to the other species. This indicates that Pm IV is functionally more different from Pm I than anticipated and that genetic distance may be a poor predictor of functional differences.…”

“…The coexistence of many cryptic species led us to hypothesize that cryptic species would have different influences on microbial enzymatic activity and on organicmatter decomposition rate. Given that Pm III is genetically (Derycke et al 2008a;Grosemans et al 2016) and ecologically (De Meester et al 2012, 2015b more distinct from the other three species, we expected that functional differences would be most pronounced between Pm III and the other cryptic species. We also tested whether a combination of all four cryptic species of L. marina would differentially affect the microbial activity and the decomposition rate of organic matter compared to single-species treatments.…”

Temperature and salinity induce differential responses in life histories of cryptic nematode species

“…In addition, interspecific interactions change when abiotic factors change (De Meester et al, 2011;De Meester et al, 2015b), which may have important repercussions for coexistence. Moreover, differences in dispersal rates between the species also have an influence on community dynamics, at least in laboratory trials (De Meester et al, 2012, 2015a. In the present study, the role of the environment has been examined by experimental variation of single isolated factors.…”

“…Our results show that these differences are also reflected in life history traits. The higher fecundity in conjunction with its comparatively good active dispersal capacity (De Meester et al, 2012) suggest that this species may be a superior disperser compared to the other three cryptic species. Differences in reproduction strategy were observed between the cryptic species: Pm II and Pm III were always oviparous in this experiment, whilst Pm I and Pm IV were mostly viviparous species (except for Pm IV under certain abiotic conditions, see Section 4.2).…”

“…This strain of E. coli has been commonly used as a single and adequate food source in different experiments with L. marina (De Meester et al, 2011, 2015ados Santos et al, 2009). Moreover, dispersal experiments showed that all 4 cryptic species are able to detect E. coli (as food source) (De Meester et al, 2012). On the 13th day of the experiment, the same amount of food was added to replenish the cultures.…”