Life history traits and demographic parameters in the Keratella cochlearis (Rotifera, Monogononta) species complex

Hydrobiologia, Jan 2018

A recent study based on DNA taxonomy indicated that the widespread rotifer Keratella cochlearis comprises several evolutionarily significant units (ESUs). Identification of ESUs based on DNA taxonomy alone is problematic and usually requires morphological, demographic, and/or ecological evidence. We isolated three haplotypes belonging to two ESUs of K. cochlearis and conducted life table experiments to investigate if this genetic diversity is reflected in demography. We found significant differences between haplotypes in life history traits (average lifespan, number of offspring, and percent of rejected eggs) and in demographic parameters (instantaneous growth rate, generation time, and net reproductive rate of the populations). During the experiments, all the haplotypes produced abnormal females with a deformed lorica, which was never reported before in K. cochlearis. We also report the first case of an amphoteric female (producing both females and males) in K. cochlearis. We hypothesize that K. cochlearis haplotypes and thus ESUs may exhibit niche differentiation through their different life histories. The link between demographic parameters of K. cochlearis and niche utilization requires further research.

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Life history traits and demographic parameters in the Keratella cochlearis (Rotifera, Monogononta) species complex

Hydrobiologia Life history traits and demographic parameters in the Keratella cochlearis (Rotifera, Monogononta) species complex 0 A. Cieplinski T. Weisse Research Department for Limnology , Mondsee , University of Innsbruck , Mondseestraße 9, 5310 Mondsee , Austria 1 A. Cieplinski (&) U. Obertegger Department of Sustainable Agro-ecosystems and Bioresources, Research and Innovation Centre, Fondazione Edmund Mach (FEM) , Via E. Mach 1, 38010 San Michele all'Adige, TN , Italy A recent study based on DNA taxonomy indicated that the widespread rotifer Keratella cochlearis comprises several evolutionarily significant units (ESUs). Identification of ESUs based on DNA taxonomy alone is problematic and usually requires morphological, demographic, and/or ecological evidence. We isolated three haplotypes belonging to two ESUs of K. cochlearis and conducted life table experiments to investigate if this genetic diversity is reflected in demography. We found significant differences between haplotypes in life history traits (average lifespan, number of offspring, and percent of rejected eggs) and in demographic parameters (instantaneous growth rate, generation time, and net reproductive rate of the populations). During the experiments, all the haplotypes produced abnormal females with a deformed lorica, which was never reported before in K. cochlearis. We also report the first case of an amphoteric female (producing both females and males) in K. cochlearis. We hypothesize that K. cochlearis haplotypes and thus ESUs may exhibit niche differentiation through their different life histories. The link between demographic parameters of K. cochlearis and niche utilization requires further research. Life table; Cryptic species; Abnormal females; Rotifers; Lake Tovel Introduction Rotifers are among the most abundant planktonic metazoans and constitute a crucial link between lower and higher trophic levels in most freshwater ecosystems around the world (Wallace et al., 2006) . Rotifer biodiversity has been studied for over two hundred years, and so far about 2000 species have been described (Koste & Hollowday, 1993; Segers & De Smet, 2008) . With the advent of molecular techniques and the introduction of DNA taxonomy, many rotifer species, traditionally considered as one species, proved to be complexes of cryptic species. Cryptic species, defined as genetically distinct but morphologically difficult-to-distinguish species (Gomez et al., 2002; Fontaneto et al., 2009; Birky et al., 2011; Obertegger et al., 2012, 2014; Cieplinski et al., 2017) , appear to be widespread among both microorganisms and macroorganisms and have been reported in many groups such as protists (Foissner, 2006), ants (Fournier et al., 2012) , harvestmen (Arthofer et al., 2013) , and rotifers (Gomez & Snell, 1996; Gomez et al., 2002; Fontaneto et al., 2009; Birky et al., 2011; Obertegger et al., 2012, 2014; Cieplinski et al., 2017) . According to the niche conservatism theory, the closer the related species are, the more profound is their niche conservatism (i.e., a higher tendency to retain their ancestral traits) and the stronger is their competition (e.g., Darwin, 1859; Violle et al., 2011) . Therefore, cryptic species should show strong interspecific competition and little co-existence (Wiens & Graham, 2005; Losos, 2008; Violle et al., 2011) . However, coexistence of closely related species is a difficult-toexplain phenomenon (Leibold & McPeek, 2006) , but has been observed in nearly 60% of rotifer complexes (Gabald o´n et al., 2017) . Yet, especially with small aquatic organisms we can never fully account for the n-dimensionality of the species niche, and, therefore, inferences about real co-existence are difficult. Evidence is growing that cryptic species in rotifers often have different life history traits despite their close phylogenetic relationship and that these differences may play a role in their co-existence in the same environment (Gabaldo´ n et al., 2015) . Consequently, our knowledge on biodiversity, biogeography, and ecology of certain species might be biased because several cryptic species with different ecological requirements and characteristics are lumped into one species. Differences in life histories of closely related species that are linked to niche differentiation may thus add to the co-existence and evolution of cryptic species (Angert et al., 2009; Montero-Pau et al., 2011) . Therefore, analyses of life histories in cryptic species complexes may help understand competitive abilities between those species. Life table experiments represent one of the most widespread methods to study life history traits and population dynamics (King, 1970; Allan, 1976; Walz, 1983, 1987; Gribble & Welch, 2013; Xi et al., 2013; Xiang et al., 2016a, b) . Life history traits are those parameters that are directly derived from the life table of an organism (Stearns, 1992). Demographic parameters (also known as ‘‘population pa (...truncated)


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Adam Cieplinski, Ulrike Obertegger, Thomas Weisse. Life history traits and demographic parameters in the Keratella cochlearis (Rotifera, Monogononta) species complex, Hydrobiologia, 2018, pp. 325-338, Volume 811, Issue 1, DOI: 10.1007/s10750-017-3499-2