Spelaeogammarus spinilacertus Koenemann and Holsinger, 2000

Bueno, Alessandra Angélica de Pádua, Bichuette, Maria Elina, Zepon, Tamires & Penoni, Ludmila Rocha, 2022, A new species of the troglobitic genus Spelaeogammarus da Silva Brum, 1975 (Amphipoda: Artesiidae) from a cave in the Brazilian semi-arid region, with new records of its congener, Spelaeogammarus spinilacertus Koenemann and Holsinger, 2000, Nauplius (e 2022020) 30, pp. 1-17 : 10-14

Spelaeogammarus spinilacertus Koenemann and Holsinger, 2000

( Fig. 6 ).

Material examined (all from Brazil, state of Bahia). 1 adult, LES 0016806, municipality of Iraquara, Buraco do Cão cave, 12°23’37.5”S 41°36’08.2”W, 20Jun. 2009, M. E. Bichuette , L. Senna-Horta colls .; 3 adults, LES 0000230 , municipality of Palmeiras , Canoa Quebrada cave, 12°25’29.6”S 41°33’28.1”W, 12 Jul. 2004, M. E. Bichuette coll.; 1 adult, LES 0000231 , municipality of Palmeiras , Canoa Quebrada cave, 12°25’29.6”S 41°33’28.1”W, 13 Nov. 2004, M. E. Bichuette coll.; 3 adults, LES 0004906 , municipality of Iraquara , Gruta da Lagoa Seca cave, 12°18’42.7”S 41°34’03.6”W, 23 Jan.2007, M. E. Bichuette coll.; 2 adults, LES0022569 , municipality of Iraquara , Gruta da Lagoa Seca cave, 12°18’42.7”S 41°34’3.6”W, 23 Jan. 2007, M. E. Bichuette coll.; 1 adult, LES 0016823 , municipality of Iraquara , Gruta Umburana cave, 12°20’25.4”S 41°36’32.0”W, 19 Jun. 2009, M. E. Bichuette coll.; 2 adults, LES 0000225 , municipality of Iraquara, Lapa Doce System, 12°20’01.7’’S 41°36’16.5”W, 30 Mar. 2005, M.E. Bichuette, D.R. Pedroso colls.; 3 adults, LES 0022568 , municipality of Iraquara, Lapa Doce System; 12°20’01.7’’S 41°36’16.5”W, 30 Oct. 2016, M.E. Bichuette, M. Rosendo, J.E. Gallão colls.; 3 adults, LES 0001804 , municipality of Iraquara, Lapa Doce System, 12°20’01.7’’S 41°36’16.5”W, 25 Mar. 2000, D. Allegrini coll.; 2 adults, LES 0027745 , municipality of Iraquara, Lapa Doce System, 12°20’01.7’’S 41°36’16.5”W, M.E. Bichuette, J.P.M. Araujo, G.H.N. Basílio, M.A. Rasteiro colls .

Identification. Taxonomic treatment followed the original description of S. spinilacertus (see Koenemann and Holsinger, 2000) and the key to Spelaeogammarus species ( Rogers et al., 2020). Spelaeogammarus spinilacertus is characterized by 4 articles on antenna 1 accessory flagellum; antenna 2 is 25 % shorter than antenna 1, flagellum with 7 segments; 6 multicuspidate setae on maxilla 1 outer plate; and 4 plumose setae on maxilliped inner plate ( Koenemann and Holsinger, 2000; Rogers et al., 2020). The original description of the species was based on one holotype and one allotype ( Koenemann and Holsinger, 2000), hampering the observation of variation. All but one diagnostic characteristic were observed on the analyzed material, i.e., instead of 6 multicuspidate setae on maxilla 1 outer plate, we found 7 setae, which could represent variability in this character.

Geographic distribution and ecological data. The distributional range of Spelaeogammarus spinilacertus increased from two (Baixa do Salitre and Jaburu caves) to seven caves (new records: Lapa Doce System, Gruta da Umburana, Gruta da Lagoa Seca, Buraco do Cão, and Canoa Quebrada caves) that define a polygon of approximately 101 km 2 ( Fig. 7C ). All caves are located in the Chapada Diamantina region, central portion of the state of Bahia, northeastern Brazil, upper Paraguaçu River basin. The limestone rocks from Chapada Diamantina region are dated to the Neoproterozoic age, and belong to the Una Geological Group, Salitre Formation ( Schobbenhaus et al., 1984). These caves present lentic water bodies of the upper phreatic zone. Spelaeogammarus spinilacertus occurs in shallow, soft-bottom pools (observations of individuals were to 2 m depth), with slow water current ( Fig. 7A, B ). Populations show a preference for swimming close to the substrate, formed mainly of silt, limestone riffles, and guano piles and, less frequently, in the mid-water and surface ( MEB., pers. obs.). The abundance is relatively high in two caves, Canoa Quebrada (observed in June/2005) and Lapa Doce System (observed in October/2016), with 40 and 20 individuals respectively.Physical and chemical variables showed little variation between the cave waters and three of them are typical of karst waters (alkaline pH and high conductivity): pH from 7.7 to 7.9; conductivity from 0.474 to 0.639 µS. cm-1; temperature from 22.5 to 26.3 ° C; and salinity from 0.1 up to 0.2 %.

We propose that Spelaeogammarus spinilacertus should be classified as Endangered ( EN) according to the IUCN criteria B 1ab(iii). The species has an extent of occurrence ( EOO) estimated less than 5,000 km 2 (criteria B 1); one location (defined as a geographically or ecologically distinct area in which a single threatening event can rapidly affect all individuals of the taxon present) (criteria a); and continuing decline in the quality of habitat (criteria b). The species is associated with phreatic water and, therefore, a single threatening event can rapidly affect the individuals of different caves. The region is influenced by several anthropogenic impacts including cattle grazing, agriculture, but the main impact could be pollution of the phreatic waters by pesticides, as the caves are located outside protected areas such as the Chapada Diamantina National Park ( Gallão and Bichuette, 2018). These impacts contribute to decline in the quality of habitat.

Spelaogammarus spinilacertus co-occurs with the troglobitic catfish Rhamdiopsis krugi Bockmann and Castro, 2010 , also endemic to limestone caves of the Chapada Diamantina ( Bichuette et al., 2015) and considered one of the predators of the amphipod species.

Figures

Figure 6.Preserved specimen of Spelaeogammarus spinilacertus Koenemannand Holsinger, 2000 fromBuraco do Cão cave, Iraquara municipality, state of Bahia, Brazil (A) and live specimen of S. spinilacertus from Canoa Quebrada cave, municipality of Iraquara, state of Bahia, Brazil (B). Photograph: (A) Luciana B.R. Fernandes, (B) Adriano Gambarini.

Figure 7. Lake formed by upper phreatic aquifer at Canoa Quebrada cave (A); small pool of upper phreatic aquifer at Lapa Doce System (B); distribution of Spelaeogammarus spinilacertus Koenemann and Holsinger, 2000, indicating caves with records of the species showing the land use and land cover of the area (C). Caption:LD = Lapa Doce System, GU = Gruta da Umburana cave, LS = Gruta da Lagoa Seca cave, BC = Buraco do Cão cave, CQ = Canoa Quebrada cave, BS = Baixa do Salitre cave, and BJ = Jaburu cave. Photographs: (A) Adriano Gambarini, (B) Jonas E. Gallão.