Growth curve of Atlantoscia floridana (van Name) (Crustacea, Isopoda, Philosciidae) from a Brazilian Restinga Forest

Abstract

The terrestrial isopod Atlantoscia floridana (van Name, 1940) occurs from the U.S.A. (Florida) to Brazil and Argentina. In the southernmost Brazilian State, Rio Grande do Sul, the species is recorded in many localities, in urban and in non-urban areas. The growth curve of Atlantoscia floridana based on field data is presented. The specimens were sampled from April, 2000 to October, 2001 at the Reserva Biológica do Lami (RBL), Rio Grande do Sul. Captured individuals were sexed and had their cephalothorax width measured, with the data analyzed with von Bertalanffy's model. The growth curves for males and females are described, respectively, by the equations: Wt = 1.303 [1 - e-0.00941 (t + 50.37)] and Wt = 1.682 [1 - e-0.00575 (t + 59.13)]. The curves showed differential growth between sexes, where females reach a higher Wµ with a slower growth rate. Based on the growth curves it was also possible to estimate life expectancy for males and females.

Growth curve of Balloniscus glaber Araujo & Zardo (Crustacea, Isopoda, Oniscidea) from Parque Estadual de Itapuã, Rio Grande do Sul, Brazil

“…1.12) was verified. This finding indicates a dimorphic body size between the sexes, as well as different growth rates, that supports the separated treatment of the curves, as performed in another study (ARAUJO & BOND-BUCKUP 2004). Life span was estimated as 28 months for males, and 36 months for females.…”

“…ACHOURI et al (2003) estimated 11 to 14 months for P. pruinosus. ARAUJO & BOND-BUCKUP (2004) found a life span of about 28 months for A. floridana females, and 18 months for males. However, analyzing the age structure of the field population, ARAUJO & BOND-BUCKUP (2005) found that the percentage of males older than 1 year was only 0.1%, whereas 1% of the females reached the 2 nd year.…”

“…Samples were hand-sorted in the laboratory, and then left in a Berleze's funnel extractor for 72 h. Individuals were separated in mancas (ARAUJO et al 2004a), males and females (ARAUJO et al 2004b), preserved in ethanol at 70%, and measured under a stereomicroscope. According to ARAUJO & BOND-BUCKUP (2004), cephalothorax width was used as a measure of size, as bodylength measurements may vary within wide ranges, depending on body contraction after death (SUTTON 1968). The curves for females and males (Fig.…”

“…Then, chosen modes were fitted in a linear regression using the method of Ford-Walford for unequal time intervals among monthly samplings (WALFORD 1946). In this regression, we considered Manca II as size at t 0 , because Manca I can be considered as the last intramarsupial stage (ARAUJO & BOND-BUCKUP 2004). The resulting coefficients a and b were used to obtain k, W ϱ , and t 0 in the following manner (FABENS 1965): k = -b; W ϱ = -a/b; t 0 = k -1 .ln[⌺(W ϱ -W t ).e (-kt) /⌺W ϱ .e (-2kt) ].…”

“…One approach to obtain this estimate is to relate age with the size of an animal's structure, which is often obtained by building growth curves (MCQUEEN & CARNIO 1974, HADDAD & VERANI 1984. The von Bertalanffy's model (VON BERTALANFFY 1938) has been successfully used for the study of the growth of peracarid crustaceans, of amphipods (DIAS & SPRUNG 2004) as well as of terrestrial isopods (Isopoda, Oniscidea) (ARAUJO & BOND-BUCKUP 2004). ACHOURI et al (2003) studied growth rates of Porcellionides pruinosus (Brandt, 1833) (Porcellionidae) at Garat Nâam (Kasserine, Tunisia), where they found different lifespan and growth rates among cohorts in a natural population.…”