Ecological traits of two Hyalella Smith, 1874 (Crustacea: Amphipoda: Hyalellidae) morphotypes from Southeastern Brazil

Abstract

The freshwater crustacean genus Hyalella is exclusive to the Americas, with a broad distribution on the neartic and neotropical regions. Because of its low dispertion ability, many species are endemic, and it is believed that the current number of known species is much inferior to the reality. Sixty-three species are registered to South America, and 28 occur in Brazil. To this day, São Paulo state presents six known species, but none of them are registered to Parque Estadual da Serra do Mar – Núcleo Santa Virgínia (PESM – NSV). Furthermore, ecological research about Brazilian Hyalella species are rare. This dissertation presents the results of a research entitled “Ecological traits of two Hyalella Smith, 1874 (Crustacea: Amphipoda: Hyalellidae) morphotypes from Southeastern Brazil”. The objective of this research was to analyze the environmental factors that allow the coexistence of two Hyalella morphotypes through niche division and the reproductive strategies of the morphotypes, based on fecundity data. Collections were held in May/2018 at PESM – NSV. Collected organisms were identified in two morphotypes (M1 and M2), and the physical habitat variables were used to observe niche division between morphotypes and life stage categories. We found 759 organisms (M1 = 356; M2 = 403). Principal Component Analysis confirmed the morphological differences between morphotypes and their division on the physical space of the streams. Covariance analysis were used to identify the physical habitat variables that most relate to each morphotype and life stage category. Morphotype 1 organisms – usually small bodied, with smaller antennas – were negatively associated to the occurrence of boulders along the transects. Females and ovigerous females were closely related to this variable; males were positively affected by mean substrate size; and juveniles did not respond to any physical habitat variable. Morphotype 2 organisms, on the other hand, were negatively affected by canopy coverage. Females and ovigerous females were dependent only upon this variable; males responded negatively to canopy coverage and positively to wetted width; and juveniles displayed preference to areas with less canopy coverage and more availability of brush and small wood debris. The mean number of eggs in the ovigerous female’s marsupium differed between morphotypes, with M2 females bearing more eggs. Mean egg volume and mean volume of eggs in the marsupium also differed between morphotypes, with M2 females carrying more voluminous eggs. In summary, the hypothesis that the two morphotypes and the different life stages occupy different niches were endorsed by our results