Planothidium victori, Novis & Braidwood & Kilroy, 2012

Novis, Phil M., Braidwood, Jasmine & Kilroy, Cathy, 2012, Small diatoms (Bacillariophyta) in cultures from the Styx River, New Zealand, including descriptions of three new species, Phytotaxa 64 (1), pp. 11-45 : 22-23

Planothidium victori sp. nov. P.M. Novis, J. Braidwood & C. Kilroy ( Figs 26–41 , 161 )

Frustules elliptic-lanceolate in valve view, monoraphid, 14.0– 16.5 µm long, 5.0– 5.2 µm wide. Frustules rotationally asymmetric to a variable degree in valve view, from almost linear to slightly curved near one pole to incised near one pole to form a hook. Striae transverse to slightly radiate at central area to more strongly radiate at poles, 14–15(–16) in 10 µm, multiseriate. Araphid valve asymmetric at central area where striae are interrupted by a “hoofmark” structure ( Fig. 40 ; sensu Round & Bukhtiyarova 1996) appressed to inner valve surface. Position of hooked pole relative to hoofmark shows that hook can occur at either pole (but never both; Fig. 38 ). Araphid valve slightly convex, raphid valve slightly concave; frustules thus curved in girdle view ( Fig. 39 ), 3.6–4.5 µm wide. Raphe straight, with expanded proximal area and terminal fissures curved towards the secondary valve side; internally, central ends are weakly curved. Sternum linear.

Type: — NEW ZEALAND: Canterbury: Styx River (lat. 43°27.800, long. 172°36.213), periphyton, P.M. Novis and J. Braidwood, 4 November 2009 ( CHR618408 !; cleaned frustules made from culture LCR-S:18:1:1) .

Distribution: —this new species is only known from site 4 in the Styx River, Canterbury, New Zealand, to date.

Etymology: —named for Victor Brown, a long-serving co-ordinator of water quality monitoring volunteers in the Styx catchment.

Molecular data: —The closest match to this strain’s 18S sequence is P. lanceolatum L1249, isolated from USA (p-distance = 0.024). The closest match to its rbc L sequence is P. frequentissimum LCR-S:2:1:1 (pdistance = 0.024; the rbc L sequence of L1249 is not available). The Styx strain formed a robust clade with L 1249 in both Bayesian and MPB analyses of 18S sequences, and a robust clade with LCR-S:2:1: 1 in both Bayesian and MPB analyses of rbc L sequences ( Fig. 161 ). The length of the 18S fragment was 428 bp, in an overall dataset 1775 bp long with 296 variable sites (161 parsimony informative, 48 occurring within the fragment from the Styx strain). The model selected by BIC and implemented in the Bayesian analysis was T92+G. The length of the rbc L fragment was 671 bp, in an overall dataset 1473 bp long with 956 variable sites (379 parsimony informative, 181 occurring with the fragment from the Styx strain). The model selected by BIC and implemented in the Bayesian analysis was GTR+G+I.

Observations: — P. victori falls within the size range of P. lanceolatum as described by Krammer & Lange-Bertalot (1991), but the non-hooked valves of P. victori are thinner and with more acutely rounded ends. The asymmetrically bent or hooked variants of this species are presumably teratological. The asymmetry occurs in frustules that are also of shorter length (so could be a result of the size limitation of asexual reproduction), since it has been postulated that diatom species can no longer initiate their sexual cycle beyond a “cardinal point” of size decrease, and many frustules below this size are reputed to become teratological ( Kociolek & Stoermer 2010). Such forms can occur as a result of physical or chemical stress during development ( Falasco et al. 2009; Kociolek & Stoermer 2010). This morphotype was found in both field material and cultures, but no other teratological forms were found for any other species under any conditions in the Styx. Although Golder Associates (2009) reported levels of Cd, Cr, and Cu above background levels about 1 km upstream of site 4, none of these exceeded the ISQG-low level (below this level, adverse effects on aquatic life are regarded as unlikely). Thus, P. victori seems particularly sensitive to contamination and may be a useful indicator species.

Although the cells resemble P. frequentissimum , which was also recovered from the Styx, the two strains clearly differed in their rbc L sequences, and in length, width, and stria density, so one is not a variant form of the other.

Order Bacillariales

Family Bacillariaceae

Figures

FIGURE 161. Bayesian phylogenies of Planothidium strains from the Styx River, for 18S rDNA (left) and rbcL (right). Support numbers above branches are Bayesian posterior probabilities / Maximum Parsimony bootstrap values. Scale bar = 0.1 subsitutions/ site. See text for substitution models and description of data sets.

FIGURE 13–41. Planothidium spp. from the Styx River. Scales: Fig. 17, 5 µm (use for 13–20, 26–39); others 1 µm. Figs 13–25. Planothidium frequentissimum strain LCR-S:2:1:1, CHR618407. Figs 13–20, Cleaned frustules viewed by LM; Figs 13–15, araphid valve showing horseshoe structure; Figs 16–18, raphid valve (vertical pairs are through-focus images of the same frustules). Figs 19, 20, variation seen in girdle view, with convex araphid valve and concave raphid valve. Figs 21–25, SEM of cleaned frustules. Fig. 21, raphid valve; Fig. 22, araphid valve with horseshoe visible; Fig. 23, internal view of araphid valve showing structure of horseshoe; Fig. 24, internal view of half of raphid valve; Fig. 25, araphid valve with depressed pseudoraphe. Figs 26–41. Planothidium victori strain LCR-S:18:1:1, CHR618408. Figs 26–39, cleaned frustules viewed by LM; Figs 26–31, araphid valve showing horseshoe structure and curved valve margin especially in smaller valves; Figs 32–37, raphid valve (vertical pairs are through-focus images of the same frustules); Fig. 38, small araphid valve with horseshoe and hooked apex showing that the valve hook can occur at either end with respect to the horseshoe (compare with 30, 31); Fig. 39, girdle view showing convex araphid valve and concave raphid valve. Figs 40, 41, SEM of cleaned frustules. Fig. 40, araphid valve with horseshoe attachment visible; Fig. 41, oblique view of raphid valve.