Population dynamics of a freshwater amphipod from South America (Crustacea, Amphipoda, Hyalellidae)

Abstract

Th is study aimed to characterize the population dynamics of Hyalella bonariensis Bond-Buckup, Araujo & Santos, 2008 from headwater spring in a rural area of state of Rio Grande do Sul, Brazil. Four samples were collected in August (winter) and October (spring) of 2012 and January (summer) and April (autumn) of 2013. Ovigerous females and precopula pairs were separated from other individual in the fi eld. A total of 5,266 specimens were sampled, being 1,878 males, 2,073 females (including 240 ovigerous females) and 1,315 juveniles. Th e frequency distribution of size classes (measured as cephalothorax length, CL) was polymodal and bimodal in males and females, respectively. Males reach larger size than females. Sexual maturity of males and females was estimated at 0.40 and 0.38 mm for CL, respectively. Total sex ratio favored females, and these were more frequent in intermediate size classes, while males were more frequent in larger size classes. Ovigerous females and couples were found in four seasons, but both were more abundant in winter. Juveniles were also found in all seasons, being more frequent in winter and spring. Th ese results showed that this H. bonariensis population has similar dynamics to other species of Hyalella Smith, 1874 from Brazil, but present variations when compared to other freshwater amphipods. keY wordsBody size, Hyalella, reproductive period, sex ratio, sexual maturity. Castiglioni et al.2

Population structure of two freshwater amphipods (Crustacea: Peracarida: Hyalellidae) from southern Brazil

“…In the last few years, understanding of American's Hyalella has risen with an increasing number of taxonomic publications, indicating that there is still a large number of species unknown to science (González and Watling, 2002a, 2002b, 2003a, 2003bBaldinger, 2004;Pereira, 2004;González et al, 2006;Cardoso et al, 2011;Bueno et al, 2013;Rodrigues et al, 2014;Cardoso et al, 2014;Colla and César, 2015). In Brazil, most studies of Hyalella concern new species descriptions (Bastos- Pereira and Bueno, 2013;Bueno et al, 2013;Cardoso et al, 2014;Bueno et al, 2014;Streck et al, 2017), however, knowledge on their life cycles, population biology e reproductive biology are limited by the studies of Castiglioni and Bond-Buckup (2008a) (Hyalella castroi González, Bond-Buckup andAraujo, 2006 andHyalella pleoacuta González, Bond-Buckup andAraujo, 2006), Castiglioni et al (2016) (Hyalella bonariensis Bond-Buckup, Araujo and Santos, 2008) and Ozga and Castiglioni (2017) Streck and Castiglioni, 2017). Most of the remaining studies published on population, reproductive, systematic, and taxonomic aspects of Hyalella species were performed with the North American species H. azteca (Cooper, 1965;Wellborn, 1994;Grosso and Peralta, 1999;Wellborn et al, 2005).…”

Population and reproductive traits of a freshwater amphipod (Crustacea, Peracarida, Hyalellidae) from northwest of the state of Rio Grande do Sul, Brazil

“…This feature may be related to the seasonal reproduction and, consequently, to the recruitment peaks in the population. This pattern of population frequency distribution is common in other species of Hyalella such as H. azteca (Pickard & Benke 1996), H. pleoacuta and H. castroi (Castiglioni & Bond-Buckup 2008a), H. bonariensis (Castiglioni et al 2016) and H. georginae and H. gauchensis (Ozga et al 2018). According to Appadoo & Myers (2004), bimodal distributions are apparently advantageous since recruitment occurs in warmer months, when food availability is higher, increasing the survival rate.…”

“…Later, individuals were identified and grouped into four categories: juveniles (specimens with undeveloped secondary sexual character), males (individuals with a well-developed gnathopod 2), females (individuals with oostegites and a small gnathopod 2), and ovigerous females (females carrying eggs or juveniles in the brood pouch) (Borowsky 1991;Castiglioni & Bond-Buckup 2008a;Castiglioni et al 2016). These amphipods were measured from the anterior margin of the rostrum until the posterior margin of the cephalothorax (head), in lateral view (cephalothorax length, CL in mm) using a micrometer eyepiece in a stereoscopic microscope.…”

“…Besides, the seasonal juvenile frequency was compared using the multinomial proportion test (MANAP; α = 0.05) (Curi & Moraes 1981). For the recruitment analysis, we considered juveniles those individuals with CL smaller than 0.27 mm (individuals where the enlargement of the second pair of gnathopods or oostegites could not be observed (Borowsky 1991;Castiglioni et al 2016) and those individuals smaller than the values estimated at sexual maturity (see values in results).…”

Population dynamics and expansion of Crangonyx pseudogracilis, a potentially invasive amphipod

“…Yet some environmental and biotic factors, could also have contributed for that, for example, a greater susceptibility of one of the genders to predation, which is directly related to the difference in sizes and behaviour. Although females of Crangonyx pseudogracilis are larger than males, males must find females to mate, thus being more exposed to predators (Jacobucci and Leite, 2006;Castiglioni et al, 2016). Additionally, a study by Watts et al (2002) revealed that the exposure of amphipods to certain chemicals present in the residual water, such as 17a À ethinylestradiol or also known as environmental estrogen (EE), can favour females more than males, resulting in a marked difference in proportions between the genders.…”