Luticola dolia Spaulding & Esposito

Kohler, Tyler J., Kopalová, Kateřina, Vijver, Bart Van De & Kociolek, J. Patrick, 2015, The genus Luticola D. G. Mann (Bacillariophyta) from the McMurdo Sound Region, Antarctica, with the description of four new species, Phytotaxa 208 (2), pp. 103-134 : 109-112

Luticola dolia Spaulding & Esposito in Esposito et al. (2008: 1385, figs. 37–41) ( Figs. 12–20 ).

LM observations:— ( Figs. 12–19 ) Valves linear-elliptic with straight to convex margins, becoming slightly undulate in larger specimens ( Figs. 12–13 ).Apices highly capitate, becoming rostrate at small sizes ( Figs. 17–19 ). Valve dimensions (n=12): length 11.3–25.1 μm, width 5.4–7.7 μm. Axial area linear, opening towards central area. An isolated pore is present in the central area, located halfway between the valve center and valve margin. Central area circular to bow-tie shaped, bordered by shortened striae on both sides. Raphe branches straight, deflecting away from isolated pore on distal and proximal ends. Transapical striae radiate throughout, 15–19 in 10 μm.

SEM observations:— ( Fig. 20 ) Striae composed of 2–3 areolae, 1–2 at apices. Areolae rounded to elongated throughout, not extending past distal raphe endings on the valve face. Isolated pore rounded. Central area bordered by single row of three rounded areolae on side opposite isolated pore, 1–2 rows on isolated pore side. Proximal raphe endings deflected opposite isolated pore, with some specimens having ends that curve back slightly to the opposite direction. Distal and proximal raphe endings terminate into linear slits or small pores on valve face. Clear separation between valve face and margins.A single row of with rounded areolae present along entire valve mantle, not interrupted at apices.

Habitat, ecology and distribution:— At present, this species is known only from the McMurdo Dry Valleys from which it was described. Even here, Luticola dolia is sparse throughout Taylor Valley, and rare or absent at Cape Royds ( Sakaeva 2014). This species has been shown to be common in the Lake Bonney Basin of Taylor Valley, especially in Wormherder Creek ( Stanish et al. 2012). In this survey, we found L. dolia to be abundant in the mosses of Lake Fryxell Basin streams, as well as the outlet of the Onyx River in Wright Valley.

INSTAAR herbarium:— Aiken Creek 901; Von Guerard Stream 905–908, 911–912, 916–918, 923, 925–926; Harnish Creek 928; Bowles Creek 933, 936, 939, 940; Wormherder Creek 955; Priscu Stream 960–961; Bohner Stream 963–966; Wharton Creek 979–982; Delta Stream 986–987, 990, 992; Onyx River 994–996, 998, 1001; Canada Stream 1010, 2257; Green Creek 1019, 1022, 1027, 2316–2317; Lawson Creek 1038, 1041; Miers Stream 1048; Adams Stream 1051, 1053–1057, 1064; Relict Channel 1066, 1068, 1070, 1077–1081, 1084; Little Sharpe (unofficial name) 2340; Upland Pond 2677–2678; Spaulding Pond 2494–2496; Picture Pond 2668.

Observations:— Identified as Navicula muticopsis f. capitata in Kellogg et al. (1980: 176, pl. 1, fig.12), L. dolia was later described as a separate species in Esposito et al. (2008). This species is easily recognizable due to the narrow constrictions beneath the highly capitate ends. It is possible that different morphotypes are present within our concept of L. dolia , as differences in distal raphe endings, density of striae areolae, valve outline, and central area shape (oval vs. bow-tie) have been observed. However, assessing differences between populations of L. dolia is difficult both due to the rarity of this taxon, but also because of the images provided in the original description, which are of intermediate lengths. Furthermore, these morphological differences are present within as well as among populations, making it difficult to discern if these represent intraspecific variation, or if two similar morphotypes co-occur. Our measurements in the above description were made from the Onyx River at Lake Vanda, which had abundant L. dolia , and is on the other side of the Asgard Range from the type locality Delta Stream ( Esposito et al. 2008), where we observed L. dolia to be more sparse. Additional SEM and LM images from the same population as those presented here are pictured on plate 138 of Levkov et al. (2013).

Luticola dolia is virtually unmistakable amongst other MDV Luticola , though it shares some similarities with Luticola taxa from other Antarctic localities. For example, Luticola doliiformis Kopalová & Van de Vijver in Kopalová et al. (2011: 49, figs. 14–28) is similar in valve outline, but differs by having broadly rounded, enlarged apices, denser striae (18–20 vs. 14 – 19 in 10 μm), and a wider axial area ( Kopalová et al. 2011). Furthermore, L. doliiformis possesses smaller, more rounded areolae compared to the larger, elongated areolae in L. dolia . Lastly, L. doliiformis possesses shorter distal raphe fissures, and has an isolated pore closer to the margin than does L. dolia ( Kopalová et al. 2011) . Luticola katkae Van de Vijver & Zidarova in Van de Vijver et al. (2011: 143, figs. 2–15) also looks similar under LM, having similar capitate apices ( Van de Vijver et al. 2011). However, L. katkae may have more areolae per stria (2–4 vs. 2–3), and is unmistakable under SEM due its elevated, thickened raphesternum, absent in L. dolia . Lastly, L. dolia shares several characteristics with L. evkae Kopalová in Kopalová et al. (2011: 51, figs. 35–50) such as similar central areas and sparse, punctate striae. However, L. dolia has a more elongated valve outline and less clearly convex margins than L. evkae . Most notably, L. evkae has broader, more capitate apices than L. dolia , as discussed in Kopalová et al. (2011).

Luticola gaussii (Heiden in Heiden & Kolbe 1928: 623, pl. 3, fig. 71) D.G.Mann in Round et al. (1990: 670) ( Figs. 21–29 , Fig. 21 is an original illustration from West & West (1911)).

LM observations:— ( Figs. 22–28 ) Valves elliptical to elliptical-lanceolate with convex margins, rounded in central area. Apices broadly rounded, capitate. Valve dimensions (n=10): length 14.8–27.5 μm, width 7.7–9.7 μm. Axial area linear, expanding towards the central area. An isolated pore present in the central area, halfway between the valve center and valve margin. Central area rectangular, bordered by shortened striae on both sides. Raphe branches straight, deflects away from the isolated pore at both proximal and distal ends. Transapical striae radiate throughout, 19–23 in 10 μm, with longitudinal interruptions present as illustrated by West & West ( Fig. 21 ).

SEM observations:— ( Fig. 29 ) Striae composed of 3–4 areolae, 2–3 at apices. Areolae elongated throughout, becoming broader near valve margins, sometimes extending past distal raphe endings. Isolated pore elongated. Central area bordered by a single row of three rounded areolae on both sides. Both proximal and distal raphe endings simple, slightly deflecting away from the isolated pore, resolving into slits on valve face. Clear separation between areolae and valve margins. A single row of elongated areolae present along entire valve mantle in shallow depression, interrupted at apices.

Habitat, ecology and distribution:— Luticola gaussii was thought to be endemic to the Antarctic continent until it was recently observed from the lakes of James Ross Island, Maritime Antarctica ( Kopalová et al. 2011). The earliest records from the McMurdo Sound region date from Cape Royds by West & West (1911) as Navicula (Pinnularia) globiceps W.Greg. (1856: 10) , and noted from Green and Clear Lakes ( Fig. 21 ). Fritch (1912) may have also found this diatom, and pictured a similar species as Navicula globiceps f. amphicephala Fritsch (1912: 54) . Luticola gaussii is a commonly reported diatom from Dry Valley streams ( Stanish et al. 2011, 2012), lakes ( Baker 1967, Spaulding et al. 1997), and ponds ( Sakaeva 2014), where it is generally rare in relative abundances (especially rare in Nostoc mats), but broad in distribution. Lastly, L. gaussii is a common Luticola species in cryoconite holes ( Stanish et al. 2013).

INSTAAR herbarium:— Aiken Creek 900–902, 2224–2228; Bowles Creek 936, 938–939; Commonwealth Stream 945–948, 951–954; Priscu Stream 961; McKay Creek 975–978; Wharton Creek 979, 981–982; Delta Stream 983, 990–991; Onyx River 995–996, 999; Canada Stream 1002–1005, 1010–1011; Green Creek 1018–1019, 1021– 1022, 1025–1026, 2314–2317; Miers Stream 1046, 1048–1049; Adams Stream 1052–1054, 1064; Picture Pond 2666– 2668, 2670; Blue Lake 2472, 2487, 2497; Many Glaciers Pond 2492; Clear Lake 2501; Coast Lake 2502; Upland Pond 2677–2678; Spaulding Pond 2494–2496; Blue Lake 2498–2500.

Observations:— Luticola gaussii was elevated to species by Hustedt ( Navicula gaussii ), and is a likely synonym with Navicula globiceps West & West (1911 : fig. 135). Navicula muticopsis f. reducta described by West & West (1911) may also be a synonym of L. gaussii , due to the image in Kellogg et al. (1980: 176, pl. 1, fig.19) [but not Seaburg et al. (1979: 166, pl. 22, fig. 92)] which is likely a small valve of L. gaussii . In the illustration provided by West & West (1911) (as Navicula globiceps ), it is clear that L. gaussii has slit-like areolae, which is confirmed by SEM ( Fig. 29 ). Also referenced by West & West (1911) in both the text and illustration are the longitudinal interruptions in striae; two in the middle of the valve, and one at the ends, which is an important distinguishing characteristic. Our measurements agree well with Levkov et al. (2013), who report the size of this species to be 14–34 μm length, 7.5–13.5 μm width, and having a stria density of 18–22 in 10 μm composed of 3–4 areolae.

Similar species include L. pseudomurrayi Van de Vijver &Tavernier in Van de Vijver et al. (2012: 164, figs. 93–110), which is often documented from East Antarctica, though not in the McMurdo Sound Region. Luticola pseudomurrayi has less capitate apices than L. gaussii , a more elongated central area, does not bear longitudinal interruptions in striae, and may have 4–5 areolae compared to 3–4 in L. gaussii ( Van de Vijver et al. 2012) . Within the McMurdo Sound Region, L. gaussii is most similar to L. transantarctica Kohler & Kopalová sp. nov., which also has highly capitate apices and convex margins. However, L. transantarctica also does not possess the longitudinal interruptions in striae, has more elongated valve margins, and is generally narrower than L. gaussii . Lastly, L. permuticopsis Kopalová & Van de Vijver in Kopalová et al. (2011: 53, figs. 51 – 72), possesses a less rounded and more elongated central part of the valve, has more areolae per striae (3–6), and more angular, capitate apices.

Figures

FIGURES 12–20. Luticola dolia Spaulding & Esposito. Light (LM) and scanning electron micrographs (SEM). 12–19. Specimens from the Onyx River, Wright Valley, LM. 20. External valve view of specimens from the Onyx River, SEM. LM scale bar = 10 μm. SEM scale bar = 2 μm (top).

FIGURES 21–29. Luticola gaussii (Heiden) D.G. Mann. 21. Original illustration from West & West (1911: pl. 26, fig. 135). Light (LM) and scanning electron micrographs (SEM). 22–28. Specimens from Coast Lake, Cape Royds, LM. 29. External valve view of specimens from Clear Lake, Cape Royds, a confirmed West & West (1911) locality, SEM. LM scale bar = 10 μm. SEM scale bar = 5 μm.