Abstract
Allometric growth of chelae dimensions was analyzed to assess the average size at the onset of morphometric maturity (ASOMM) and sexual dimorphism regarding the pair of chelae in the Aegla castro. Both adult males and females are heterochelous with the most robust chela occurring predominantly on the left side. Both chelae are larger in males than they are in females of similar size, thus characterizing these structures as sexually dimorphic traits. The ASOMM estimated for males and females were 10.91 and 10.03 mm of carapace length (CL), respectively. The increase in variability of chelae dimensions in post-pubertal males led to the recognition of two morphotypes (I and II). Temporal variation in the proportions of morphotype II males in relation to females showing late ovarian development was synchronous, making the sexually functional nature of these males evident. The average size at the onset of functional maturity (ASOFM) estimated for males (based on the transition from morphotype I to morphotype II) and females (based on the detection of late ovarian development or eggs) were 17.12 and 12.59 mm of CL, respectively. Ovigerous females were sampled from April through August 2007, characterizing a marked seasonal reproductive period lasting for 5 months.
Highlights
Aegla is unique among anomurans because all 78 species described so far are endemic to continental South America from latitude 70°S, in Chile to latitude 20°S in Brazil (Bueno et al, 2007; Oyanedel et al, 2011), and are entirely adapted to freshwater habitats, such as lakes, rivers and streams (Schmitt, 1942; Martin and Abele, 1988; Bond-Buckup and Buckup, 1994)
We report the occurrence of sequential adult male morphotypes and their relationship with the reproductive cycle in the population
The relationship between the two carapace measurements taken were described by a single linear function equation Carapace length with rostrum included (CLR) = 1.173CL + 0.176 (r2 = 0.9990) since the relationship did not differ significantly between sexes [analysis of covariance (ANCOVA): F= 1.441; p = 0.2306 and F 0.9701; p = 0.3251]
Summary
The family Aeglidae Dana, 1852 includes two extinct genera from marine sediment from the Pacific region, Haumuriaegla Feldmann, 1984 and Protaegla Feldmann, Vega, Applegate & Bishop, 1998, and one extant genus, Aegla Leach, 1820 found in freshwater habitats (Feldmann, 1984; Bond-Buckup and Buckup, 1994; Feldmann et al, 1998; Bond-Buckup et al, 2008; McLaughlin et al, 2010).Aegla is unique among anomurans because all 78 species described so far (see checklist by McLaughlin et al, 2010, augmented by description of new species published afterwards by Santos et al, 2012; 2013; 2014; 2015) are endemic to continental South America from latitude 70°S, in Chile to latitude 20°S in Brazil (Bueno et al, 2007; Oyanedel et al, 2011), and are entirely adapted to freshwater habitats, such as lakes, rivers and streams (Schmitt, 1942; Martin and Abele, 1988; Bond-Buckup and Buckup, 1994). The family Aeglidae Dana, 1852 includes two extinct genera from marine sediment from the Pacific region, Haumuriaegla Feldmann, 1984 and Protaegla Feldmann, Vega, Applegate & Bishop, 1998, and one extant genus, Aegla Leach, 1820 found in freshwater habitats (Feldmann, 1984; Bond-Buckup and Buckup, 1994; Feldmann et al, 1998; Bond-Buckup et al, 2008; McLaughlin et al, 2010). Allometric growth analysis has been often employed in determining the average size at the onset of morphometric maturity of aeglids species (Colpo et al, 2005; Viau et al, 2006; Bueno and Shimizu, 2009; Oliveira and Santos, 2011; Trevisan and Santos, 2012; Copatti et al, 2015)
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