Population biology of Aegla platensis (Decapoda: Anomura: Aeglidae) in a tributary of the Uruguay River, state of Rio Grande do Sul, Brazil

Abstract

ABSTRACT. Aeglids are freshwater anomurans that are endemic from southern South America. While their population biology at the species-level is relatively well understood, intraspecific variation within populations has been poorly investigated. Our goal was to investigate the population biology of Aegla platensis Schmitt, 1942 from the Uruguay River Basin, and compare our data with data from other populations. We estimated biometric data, sex ratio, population density and size-class frequencies, and frequencies of ovigerous females and juveniles, from the austral spring of 2007 until autumn 2008. Sexual dimorphism was present in adults, with males being larger than females. Furthermore, males and females were significantly larger than previously recorded for the species. The overall sex ratio was 1.33:1 (male:female), and population density ranged from 1.8 (spring) to 3.83 ind.m -² (winter). Data from this population differ from published information about A. platensis in almost all parameters quantified except for the reproductive period, which happens in the coldest months, and a population structure with two distinct cohorts. Difference among studies, however, may be in part due to methodological differences and should be further investigated in order to determine their cause. In addition to different methodologies, they may result from ecological plasticity or from the fact that the different populations actually correspond to more than one species.

Method of capture and population structure of Aegla georginae Santos and Jara, 2013 (Decapoda: Anomura: Aeglidae) in a tributary of the Ibicuí River in southern Brazil

“…Females or juveniles would not enter the traps to avoid agonistic encounters with the larger males (Trevisan and Santos, 2014). Similar to this study, Dalosto et al (2014) also found that individuals were significantly greater in size in trap captures than in handnet captures. Furthermore, sexual dimorphism, with males larger than females (CL, CW, AW, LSQ, LMQ, and HMQ), was verified for grouped data and trap captures, but not for handnet capture ( Table 2).…”

“…Other studies on the size of male and female aeglids are also possibly influenced by the capture method (Table 4), which demonstrates the importance of considering the capture method in the evaluation of sexual dimorphism. Similar to this current study, Dalosto et al (2014) compared the use of traps with handnets and also found that the males were significantly greater in size than the females only in the trap captures.…”

“…Trevisan and Santos (2014) and Dalosto et al (2014) also analyzed capture methods in the assessment of the relative abundance for A. manuinflata and A. platensis, respectively. Differences according to capture method were found by Trevisan and Santos (2014), but not by Dalosto et al (2014). Other studies using handnets or even manual efforts in capturing aeglids also found a relative abundance of 1:1 for A.…”

“…Information about the population structure is important in working with decapods because the data assist in understanding the biology of the species in a given ecosystem. Population aspects in aeglids have been described by several authors in rivers located in the Atlantic Forest in Brazil such as Aegla paulensis Schmitt, 1942(Lopez, 1965, Aegla perobae Hebling and Rodrigues 1977 (Rodrigues andHebling, 1978), Aegla leptodactyla Rossi, 1977 (Noro andBuckup, 2002), Aegla castro Schmitt, 1942 (Swiech-Ayoub andMasunari, 2001;Fransozo et al, 2003), Aegla longirostri Buckup, 1994 (Colpo et al, 2005), Aegla franciscana Rossi, 1977 (Gonçalves et al, 2006), Aegla schmitti Hobbs III, 1979(Teodósio and Masunari, 2009), Aegla parana Schmitt, 1942(Grabowski et al, 2013, Aegla platensis Schmitt, 1942 (Bueno andDalosto et al, 2014), Aegla manuinflata Bond-Buckup and Santos, 2009 (Trevisan and and A. platensis, Aegla grisella Bond-Buckup and Buckup, 1994 and Aegla ludwigi Jara, 2013 (Copatti et al, 2015).…”

“…Usually, in studies of the population structure of aaeglids have not compared different capture methods, although Trevisan and Santos (2014) and Dalosto et al (2014) have considered the capture methods in the evaluation of relative abundance of A. manuinflata and A. platensis, respectively. We agree that the capture methods influence the evaluation of the population structure of aeglids.…”