High biological species diversity in the arctic flora

Abstract

The arctic flora is considered to be impoverished, but estimates of species diversity are based on morphological assessments, which may not provide accurate counts of biological species. Here we report on crossing relationships within three diploid circumpolar plant species in the genus Draba (Brassicaceae). Although 99% of parental individuals were fully fertile, the fertility of intraspecific crosses was surprisingly low. Hybrids from crosses within populations were mostly fertile (63%), but only 8% of the hybrids from crosses within and among geographic regions (Alaska, Greenland, Svalbard, and Norway) were fertile. The frequent occurrence of intraspecific crossing barriers is not accompanied by significant morphological or ecological differentiation, indicating that numerous cryptic biological species have arisen within each taxonomic species despite their recent (Pleistocene) origin.crossing relationships ͉ cryptic species ͉ Draba ͉ speciation ͉ postmating isolation T he Arctic f lora has long been viewed as depauperate.Indeed, the decrease in biological diversity with increasing latitude is one of the oldest recognized patterns in ecology (1). Diversity has, however, typically been quantified as the number of morphological or ''taxonomic'' species. Little is known about biological species diversity in the Arctic (2), because the recognition of biological species requires information on reproductive isolation.Here we present results from crossing experiments within three diploid circumpolar plant species: Draba fladnizensis, Draba nivalis, and Draba subcapitata (Table 1, which is published as supporting information on the PNAS web site). Low levels of genetic differentiation within and among the species suggest they originated recently, probably within the last one million years (3). The species are mainly self-pollinated (4), but they occasionally outcross as demonstrated by reports of natural hybrids between D. fladnizensis and D. nivalis (5). We show that, contrary to expectations based on observations of limited morphological, ecological, and genetic diversity, numerous cryptic biological species have arisen within each of the taxonomic species studied here. These results imply that biological species diversity may be considerably higher in arctic regions than previously believed. ResultsAll of the 79 parental plants of D. fladnizensis and D. nivalis and six of the seven parental plants of D. subcapitata were highly fertile ( Table 1). The within-population crosses mostly generated fertile hybrids (10 of 16 crosses attempted), but six crosses resulted in semisterile hybrids (Tables 2 and 3, which are published as supporting information on the PNAS web site). The within-region crosses (among populations in Alaska) generated hybrids that were semisterile in D. fladnizensis ( Fig. 1 and Tables 2 and 3) and mostly sterile in D. nivalis (Fig. 2 and Tables 2 and 3). Likewise, the majority of crosses among regions resulted in sterile Correlations between geographic and genetic amplified fragment length polym...

Evolution of reproductive isolation in plants

“…Both, A. thaliana and the investigated arctic Draba, are highly selfing which may explain the occurrence and maintenance of strong postzygotic barriers within species, because selfing provides strong premating isolation, thereby facilitating the accumulation of hybrid incompatibilities by genetic drift (Grundt et al, 2006). But intraspecific polymorphisms for hybrid sterility factors are not restricted to highly selfing species.…”

“…In rice, a major crop species, several hybrid sterility and inviability factors have evolved after the separation of indica and japonica subspecies, possibly as consequence of (Harushima et al, 2002). In arctic Draba, partial to complete hybrid sterility was found in some intraspecific crosses despite full fertility of the parental plants (Grundt et al, 2006). The sterile, intraspecific hybrids had regular meiosis that makes major chromosomal differences an unlikely cause of the sterility barriers.…”

“…The sterile, intraspecific hybrids had regular meiosis that makes major chromosomal differences an unlikely cause of the sterility barriers. Instead, a genic basis brought about by Bateson-Dobzhansky-Muller (BDM) incompatibilities was suggested (Grundt et al, 2006). In the model plant species Arabidopsis thaliana, about 2% of intraspecific crosses give progeny that suffer from hybrid necrosis caused by epistatic interactions among loci and thus by BDM incompatibilities.…”

Revealing the hidden niches of cryptic bumblebees in Great Britain: Implications for conservation

“…The development of molecular genetic tools has enabled the detection of numerous cryptic species. Large genetic distances within traditionally recognised species, usually in combination with morphological, geographical, ecological or behavioural differences, have led to the discovery of cryptic species in a diverse range of organisms, from tropical butterflies (Hebert et al, 2004), to arctic flora (Grundt, 2006), fish (Feulner et al, 2006;Puckridge, 2013) and lemurs (Ravaoarimanana et al, 2004).…”

High mountain origin, phylogenetics, evolution, and niche conservatism of arctic lineages in the hemiparasitic genus Pedicularis (Orobanchaceae)

“…Arctic in situ speciation has also been documented, for example, in Artemisia, Cerastium, Douglasia, Draba, Ranunculus, and Saxifraga (e.g., Brochmann et al, 1998;Grundt et al, 2006;Hoffmann et al, 2010;Jørgensen et al, 2006;Scheen et al, 2004;Schneeweiss et al, 2004;Tkach et al, 2008aTkach et al, , 2008b.…”