Models of ontogenetic allometry in cladoceran morphology studies

Abstract

Ontogenetic variation of morphological traits in cladocerans is usually analysed by a simple allometry function. We found that common cyclomorphic and inducible traits in Bosmina and Daphnia sometimes deviate from simple allometry, however. Consequently, simple allometric analysis may at times be inadequate since important aspects of the ontogenetic development may not be revealed. We suggest that other allometric models should be used more extensively in ontogenetic studies of cladocerans morphology. Especially, complex allometric functions may help analyse the effects of sizeselective predation on morphological defence traits when predators prefer prey of intermediate size.

Size variation of morphological traits in Bosmina freyi and its relation with environmental variables in a tropical eutrophic reservoir

“…Melão, M. G. (1999) 28 mentioned that temperature increase is a factor that directly affect organism's life cycle and population attributes, causing a time decrease in the organism's growth and an increase in population growth rates, which favors large populations with small size individuals 29 , such as we observed in this study in the riverine zone and in the reservoir subsurface, where occurred the highest number of individuals with youth traits and higher mucron and antennule lengths 30 .…”

“…The highest abundance of more significant individuals and smaller mucron and antennule lengths tended to coincide with the increase of Cryptomonas sp biomass in the zone near the dam (lacustrine zone), the photic zone boundary. The last implies that maybe these genera of algae constitute an essential resource for adults of B. freyi 30 in the reservoir 24 said that nanoplanktonic and mixotrophic species of Cryptophyta are a persistent component of zooplankton diet from The Riogrande II reservoir; apparently, it favors its growth and reproduction rates because it provides enough organic carbon, nitrates, and phosphates. Furthermore, it is very feasible that B. freyi complements its diet with detritus 42 and that alimentary strategy becomes more critical on small individuals of B. freyi together with the dissolved substances and organisms of picoplankton ingestion (< 2 µm).…”

Turning inducible defenses on and off: adaptive responses of Daphnia to a gape‐limited predator

“…In the case of Daphnia-Chaoborus interactions, the sizes of both predator and prey determine the effectiveness of neck spines as induced defenses. This effectiveness can be negated if the predator's mouth gape is very large relative to the size of the prey (Lagergren et al 2007). For very small (0.65 mm) Daphnia, neck spines were completely ineffective in preventing predation by fourthinstar Chaoborus trivittatus (Fig.…”

“…This pattern occurs because predator strike efficiency is determined by the interaction between prey body size and the induced defense. If the induced defense is ineffective in small prey, delaying its formation to a later stage will increase fitness by reducing the costs of the defense (Lagergren et al 2007). If large prey have low vulnerability due to their size, the added presence of an induced defense may be more costly than beneficial, and at some point increased body size will make the prey invulnerable and the induced defense useless.…”

Exotic species of zooplankton in the Upper Paraná River floodplain, Daphnia lumholtzi Sars, 1885 (Crustacea: Branchiopoda)

“…This species has long spines and projections in its head that are peculiar because they reduce the vulnerability to predation by planktivorous fishes and invertebrates, furnishing an advantage over other Daphnia species (Lagergren et al, 2007). However, Johnson and Havel (2001) observed that D. lumholtzi may coexist with other daphniids, in temperate regions due to little seasonal overlap with native daphniids.…”