Holopedium acidophilum, Rowe, Chad L., Adamowicz, Sarah J. & Hebert, Paul D. N., 2007

Rowe, Chad L., Adamowicz, Sarah J. & Hebert, Paul D. N., 2007, Three new cryptic species of the freshwater zooplankton genus Holopedium (Crustacea: Branchiopoda: Ctenopoda), revealed by genetic methods, Zootaxa 1656, pp. 1-49 : 32-34

Holopedium acidophilum n. sp.

Etymology. acidophilum refers to the apparent restriction of populations of this species to acidic bogs, ponds, and lakes.

Type locality. Red Rock Pond, New Brunswick, Canada (45.233º N, 66.733º W), which is located near St. George, NB. It is situated north of Lake Utopia. From Hwy 785, turn onto Red Rock Lake Road. This road bifurcates 3.5 km later. Take the right fork. Proceed 2.9 km to Red Rock Pond which is on the right hand side of the gravel road.

Type specimens. Holotype: an ovigerous female in ethanol deposited in the CMN under accession number CMNC 2007-0738 (collection date June 13, 1992).

Paratypes: 10 ovigerous females, preserved in ethanol, deposited in the CMN under accession number CMNC 2007-0739 (collection date June 13, 1992).

Material examined. Other habitats with H. acidophilum are listed in Appendix A.

Morphological description. FEMALE. Representative photomicrographs are shown in Fig. 9 . The jelly coat is of the A type, in which the anterior jelly curl arches toward the anterior portion of the jelly coat, and the lateral lobes are undivided (see Montvilo et al. 1987).

Adult carapace lengths range from 0.62–1.46 mm (mean 1.10 mm), while carapace heights range from 0.24–1.48 mm (mean 1.08 mm). The H/L ratios range from 0.40–1.29 (mean 0.97). The ventral carapace margin is ordinarily spinulated posteriorly, but smooth anteriorly. Individuals lacking spinulation along the entire ventral valve margin were encountered.

Anal spine number ranges from 8–21 (mean 14.07). Holopedium acidophilum lacks a basal spine on each postabdominal claw. Each claw invariably has a row of denticles running laterally from the base of the claw to its midpoint.

MALE. Males were found in the type locality (Red Rock Pond, NB) from collections made in June and September over several years. Body lengths range from 0.40–0.91 mm. The ventral carapace margin is spinulated posteriorly, but smooth anteriorly.

Males possess 9–17 anal spines. Holopedium acidophilum lacks a basal spine on each postabdominal claw. Each claw invariably has a row of denticles running laterally from the base of the claw to its midpoint.

Differential diagnosis. H. acidophilum can be distinguished from H. amazonicum and H. atlanticum by its larger size and greater number of anal spines. It differs from both members of the H. gibberum species complex by its lack of a basal spine on the postabdominal claw. Holopedium acidophilum can be biochemically distinguished from H. atlanticum at the Pgm locus. Holopedium acidophilum possesses an allele that migrates faster than the allele present in H. atlanticum . COI mtDNA sequence divergence between H. acidophilum and H. amazonicum averages 8.7%, while the divergence between H. acidophilum and H. atlanticum averages 10.6%. Based on current evidence, individuals showing less than 6% divergence from a representative COI mtDNA sequence (GenBank AF 245352 ) belong to H. acidophilum .

Distribution. Holopedium acidophilum appears to be restricted to a narrow latitudinal range (43º to 47º N) spanning North America ( Fig. 4 d). This species was not found to co-occur with other species of Holopedium . Despite concentrated sampling within this range, this species was found rarely. It occurred in three lakes and one pond on the west coast of Oregon, a small pond on the upper Michigan peninsula, and two bogs in southeastern New Brunswick. The eastern bog habitats were situated within a few kilometers of lake populations of both H. glacialis and H. atlanticum , but there was no evidence of genetic exchange as indicated by distinctive allozyme and mtDNA profiles. In the west, H. acidophilum was found in coastal lakes and ponds in Oregon, while the nearest populations of H. glacialis were in lakes in the Coastal Mountains.

Breeding system. Males were detected in the eastern populations in mid June and late September, indicating that members of these populations are cyclical parthenogens. Males were not detected in western and central populations, but this was likely because they were sampled in the summer. Moreover, genotype frequencies were generally concordant with Hardy-Weinberg expectations.

Figures

FIGURE 4. Putative geographic distribution of Holopedium species. Dots indicate populations where species assignments were confirmed by genetic analyses. Dark shaded areas represent the hypothesized range of each species based on results from this study and from distribution data from 1,827 localities inhabited by Holopedium, obtained from literature reports or by sampling (see Rowe 2000). Since several species are morphologically cryptic while the species complexes can be readily distinguished, the areas between or adjacent to genetic localities are tentatively marked as that same species, provided that there are Holopedium records there belonging to the same complex. Pending further evidence, all South American localities are here shaded as H. amazonicum and most Eurasian localities as H. gibberum s. s., but further cryptic species may be detected in the future. Definitive species assignments for populations in Greenland and India, which are currently described as separate species, require genetic evidence (see text), but morphological traits indicate that they do belong to the H. gibberum complex. Their distributions are shown along with H. gibberum s. s. (inset map in part b). a) H. glacialis n. sp., b) H. gibberum s. s., c) H. atlanticum n. sp., d) H. acidophilum n. sp., and e) H. amazonicum s. s.

FIGURE 9. Representative photomicrographs of Holopedium acidophilum. (a, b) Lateral view of female in jelly coat stained with dilute fuschain red. (c) Lateral view of female head and anterior jelly curl. Jelly coat stained with dilute fuschian red. (d) Lateral view of female abdomen. (e, f) Lateral views of female postabdomen (g) Lateral view of female postabdomen, Red Rock Pond, New Brunswick, June 1, 1992. (h) Lateral view of brood pouch margin and eggs. (i) Lateral view of ventral carapace spinules. (j, k) Lateral views of male with jelly coat removed. (l) Frontal view of male biramous antennae. (m) Lateral view of hook on first thoracic limb of male. (n) Lateral view of male postabdomen. (a – c, h, j – n) from Red Rock Pond, New Brunswick, June 15, 1994. (d – f, i) from Saunders Pond, Oregon, April 16, 1993.