Area and the rapid radiation of HawaiianBidens(Asteraceae)

Abstract

Aim To estimate the rate of adaptive radiation of endemic Hawaiian Bidens and to compare their diversification rates with those of other plants in Hawaii and elsewhere with rapid rates of radiation. Location Hawaii. Methods Fifty‐nine samples representing all 19 Hawaiian species, six Hawaiian subspecies, two Hawaiian hybrids and an additional two Central American and two African Bidens species had their DNA extracted, amplified by polymerase chain reaction and sequenced for four chloroplast and two nuclear loci, resulting in a total of approximately 5400 base pairs per individual. Internal transcribed spacer sequences for additional outgroup taxa, including 13 non‐Hawaiian Bidens, were obtained from GenBank. Phylogenetic relationships were assessed by maximum likelihood and Bayesian inference. The age of the most recent common ancestor and diversification rates of Hawaiian Bidens were estimated using the methods of previously published studies to allow for direct comparison with other studies. Calculations were made on a per‐unit‐area basis. Results We estimate the age of the Hawaiian clade to be 1.3–3.1 million years old, with an estimated diversification rate of 0.3–2.3 species/million years and 4.8 × 10−5 to 1.3 × 10−4 species Myr−1 km−2. Bidens species are found in Europe, Africa, Asia and North and South America, but the Hawaiian species have greater diversity of growth form, floral morphology, dispersal mode and habitat type than observed in the rest of the genus world‐wide. Despite this diversity, we found little genetic differentiation among the Hawaiian species. This is similar to the results from other molecular studies on Hawaiian plant taxa, including others with great morphological variability (e.g. silverswords, lobeliads and mints). Main conclusions On a per‐unit‐area basis, Hawaiian Bidens have among the highest rates of speciation for plant radiations documented to date. The rapid diversification within such a small area was probably facilitated by the habitat diversity of the Hawaiian Islands and the adaptive loss of dispersal potential. Our findings point to the need to consider the spatial context of diversification – specifically, the relative scale of habitable area, environmental heterogeneity and dispersal ability – to understand the rate and extent of adaptive radiation.

Rapid adaptive radiation and host plant conservation in the Hawaiian picture wing Drosophila (Diptera: Drosophilidae)

“…Among important Drosophila hosts, only the lobeliad radiation (Campanulaceae) has been dated, to 13 Mya (Givnish et al, 2009). The majority of other Hawaiian plant groups that have been dated arrived 4-5 Mya when Kauai was the primary high island, or more recently (Knope et al, 2012;Price and Clague, 2002;Sebastian et al, 2012;Willyard et al, 2011). It is notable that within the picture wing clade, the basal adiastola group is both the only one to branch off prior to the origin of Kauai, and almost exclusively utilizes lobeliads as hosts .…”

Multiplexed‐shotgun‐genotyping data resolve phylogeny within a very recently derived insular lineage

“…Thus, the results presented here suggest that analyses of MSG data can provide the much-needed phylogenies for comprehensive evolutionary studies of Macaronesian endemic plants. Given the estimated ages of radiations on other archipelagos-e.g., Bidens (3.1-1.3 Mya, Knope et al, 2012 ), silverswords (5.2 Mya, Baldwin and Sanderson, 1998 ), lobeliads (13.6 ± 1.5 Mya, Givnish et al, 2009), and honeycreepers (5.7 Mya, Lerner et al, 2011) in Hawaii, and Geospiza (2.3 Mya, Sato et al, 2001 from the Galapagos-it is very likely that MSG data will prove similarly useful in a variety of groups in different oceanic archipelagos.…”

“…Some 60% of the world's 34 biodiversity hotspots include islands ( Myers et al, 2000 ), and somewhere between 8 and 14% of insular plant endemics are in danger of extinction ( Caujapé-Castells et al, 2010 ). For the past three decades, oceanic island plants have been prominent subjects of studies utilizing various molecular markers, with one of the early and continuing results being a "decoupling" of variation between ecological/morphological characters and molecular variation, with minimal divergence in the latter despite extensive variation in the former ( Lowrey et al, 2001 ;Givnish et al, 2009 ;Knope et al, 2012 ). A pronounced case of such decoupling occurs in the small genus Tolpis (Asteraceae; Fig.…”

Profuse evolutionary diversification and speciation on volcanic islands: transposon instability and amplification bursts explain the genetic paradox

“…The products of such adaptive radiations frequently arise rapidly [13, 40], and exhibit much greater phenotypic variation than observed in the rest of the world for the genus or lineage [8]. Yet paradoxically, they show lower rates of structural gene evolution than expected [13, 119].…”