Morphological variation of Keratella cochlearis (Gosse) in Myanmar (Burma) in relation to zooplankton community structure

Abstract

Keratella cochlearis was present in 27 of 35 water bodies sampled in Myanmar, and was the most abundant rotifer in 10. Measurements of lorica length and posterior spine length from 20 localities showed that posterior spine length varied both with lorica length and with the composition of the crustacean zooplankton. Long spines were associated with dominance by Heliodiaptomus. The shortest spines were found in samples dominated by cladocerans or cyclopoid copepods. Posterior spine length was positively correlated with the number of diaptomid copepods. Forms without posterior spines were found in 17 localities. The lorica lengths of these spineless forms were generally similar to those of co-occurring spined forms (r = 0.68), but in a few samples the loricas of the spineless forms were significantly larger. These larger forms are similar to the 'aspina' forms recently recognised in the River Thames in England. These samples were dominated by cladocerans or cyclopoid copepods. In one locality spineless forms were found without spined forms. The crustacean zooplankton in this locality was also dominated by cladocerans.

Intraspecific variation in sensitivity to food availability and temperature-induced phenotypic plasticity in the rotiferKeratella cochlearis

“…The morphological differences between the two clone populations in our study are consistent with the general consensus that K. cochlearis in lakes with lower food availability (e.g. Tinaja lake) tend to be longer and have longer spines than those living in eutrophic conditions (Hillbricht-Ilkowska, 1972;Diéguez et al, 1998;Green, 2007). The fitness benefit of a longer PSL in the Tinaja clone is likely to be a reduced sinking rate (Stemberger, 1990;Zagarese and Marinone, 1992).…”

“…The PSL and lorica size of K. cochlearis can also affect fitness and competitive ability. There is a general consensus from field observations that K. cochlearis tends to be longer and have longer spines in lakes with lower versus higher food availability (Hillbricht-Ilkowska, 1972;Green, 2007;Gopko and Telesh, 2013). However, the specific effect of temperature could not be controlled in these studies.…”

High diversity in Keratella cochlearis (Rotifera, Monogononta): morphological and genetic evidence

“…ESUs 3 and 6, respectively). Hofmann (1983) and Green (2005Green ( , 2007 noted that tecta specimens could not be explained by allometric growth because specimens with spines were smaller than those without spines. Green (2005) presented three hypotheses of the origin of spineless K. cochlearis: 1, true tecta (appearing only in colder periods of the year as the ''end'' of the posterior spine reduction); 2, aspina (truly spineless, absent in the winter, LL longer than in spined form); 3, ecaudata (the same dorsal structure, occurring in summer, LL longer than in spined form).…”

“…Especially, the presence and length of the posterior spine seems to be a morphological character whose suitability for discriminating species is questionable. In eutrophic habitats, K. cochlearis tends to be smaller and has smaller posterior spines than in oligotrophic habitats (Green, 2007).…”

Evolution of a primary consumer in response to low and high food availability shapes life history traits and population demography

“…In contrast, during the restoration of lake ecosystems, both nutrient concentration and phytoplankton abundance decrease, and large-sized species gradually replace small-sized species in zooplankton communities. Other than the decreased predation efficiency of fish, low edible algal density is considered to be main reason for succession of zooplankton communities (Die ´guez et al, 1998;Green, 2007;Jeppesen et al, 2007;Louette et al, 2009;Qin, 2009;Zeng et al, 2017). From a microevolutionary perspective, these zooplankton populations can adapt to low algal densities in oligotrophic lakes, and high algal densities in eutrophic lakes (Scheuerl & Stelzer, 2013;Declerck & Papakostas, 2017), but experimental evidence for this is scarce (Ramos-Rodrı ´guez et al, 2020).…”