Patterns of differentiation in the life history and demography of four recently described species of the Brachionus calyciflorus cryptic species complex

Abstract

Brachionus calyciflorus is arguably the most studied freshwater monogonont rotifer. Although it has been recognised as a cryptic species complex for more than a decade, a formal (re‐)description of the four species known so far (B. calyciflorus, Brachionus dorcas, Brachionus elevatus, and Brachionus fernandoi) has only recently been made. Information on the ecology of these species is very scant and fragmented. The aim of this study was to test for ecological divergence between these four species, specifically their life history strategy and population demography. We conducted a life history experiment using 12–16 genotypes per species. For each species, genotypes were extracted from at least three different natural populations. In addition, we performed population‐level culture experiments with the aim to compare population growth rates and demographic structure of experimental populations among species. Finally, we searched the literature for life history studies with molecular data allowing retrospective species identification. We found pronounced differences in life history traits between B. fernandoi and the other three species. B. fernandoi had higher egg and juvenile development times and a lower egg production rate and mictic ratio. We detected no significant life history differences among B. calyciflorus, B. elevatus, and B. dorcas. Population growth rates of B. fernandoi and B. calyciflorus were higher than those of B. elevatus and B. dorcas. Life history divergence resulted in marked differences in the demographic structure of populations. Populations of B. fernandoi contained larger fractions of pre‐reproductive females and lower fractions of adult females with sexual eggs than populations of B. calyciflorus, B. elevatus, and B. dorcas. Mortality was found to be highest in B. elevatus and lowest in B. calyciflorus populations. Our results show that a reverse taxonomy approach is powerful in revealing sources of variation in ecologically relevant traits of cryptic species, such as life history and demographic structure. Explicit consideration of this variation is crucial for future studies of their dynamics in natural communities.

Patterns of Rotifer Diversity in the Chihuahuan Desert

“…Our analyses also show that rotifer assemblages are correlated with distance at smaller spatial scales but are more homogenous at the regional level (Table 4). Other papers have reported similar patterns in multiple studies analyzing species assemblages or populations of a single species [147,160,[163][164][165][166][167]. Thus, our results seem to support the Baas Becking Principle-"Everything is everywhere, but, the environment selects"-the ubiquity hypothesis [168].…”

“…The five species with significant indicator values associated with a combination of five habitat types (L. bulla, P. megalotrocha, L. luna, and C. gibba) possess wide ecological tolerances. Another implication is that these morphospecies likely represent cryptic species complexes [159,160] (see below).…”

Inter- and intraspecific differences in rotifer fatty acid composition during acclimation to low-quality food

“…Recently, experiments with the two closely related rotifer species Brachionus calyciflorus sensu stricto (s.s.) and Brachionus fernandoi feeding on diets differing in biochemical food quality revealed not only species-specific, but also strainspecific differences in fitness responses, such as population growth, fecundity and survival [35]. Differences in life-history traits between B. calyciflorus s.s. and B. fernandoi feeding on an alga that lacks LC-PUFA have also been demonstrated by Zhang et al [36]. These differences among rotifer strains and species suggest that biochemical constraints may act as evolutionary drivers on physiological traits within the genus Brachionus.…”

Temperature-dependent life history and transcriptomic responses in heat-tolerant versus heat-sensitive Brachionus rotifers

“…Differences in life histories between sibling species of the B. calyciflorus species complex have been found in response to competition and/or predation risk 84 . A recent study 85 performed under stable food and temperature conditions (24 °C) showed differences in life history traits such as egg and juvenile developmental times, and egg production between these species. As a corollary, they demonstrated that observed differences are consistent across tested clones within species, i.e., they really represent differentiation between the species.…”