Evaluating the Qualitative Effectiveness of a Novel Pollinator: a Case Study of Two Endemic Hawaiian Plants

In situations where native mutualists have become extinct, non‐native species may partner with remnant native species. However, non‐native mutualists may differ behaviorally from extinct native mutualists. In the case of pollination, novel relationships between natives and non‐natives could differ both quantitatively and qualitatively from native–native relationships. In Hawai'i, the non‐native Japanese White‐eye (Zosterops japonicus) has largely replaced endemic birds as pollinator of the endemic Clermontia parviflora and C. montis‐loa. We surveyed Clermontia patches and found that they ranged from 106 to 1198 m in diameter. We performed manual pollination of flowers with pollen taken from plants at five distance categories, ranging from 0 (self‐fertilization) to 20 km, and examined the germination of resulting seeds. We used radiotelemetry to estimate daily Japanese White‐eye movement distances. Percent germination of seeds after short‐ to intermediate‐distance pollination crosses (i.e., 20–1200 m, or intra‐patch pollen transfer distances) significantly exceeded germination of seeds from selfed trials for C. parviflora. No significant differences in germination rates among treatments were detected for C. montis‐loa. The maximum daily movement distances of radio‐tracked birds were generally <1 km. Together, these results suggest that this novel pollinator may be an effective mutualist for both Clermontia species. This study serves as an example of research examining qualitative components of novel mutualism, which are generally neglected relative to quantitative components.     

The ecological consequences of megafaunal loss: giant tortoises and wetland biodiversity

The giant tortoises of the Galápagos have become greatly depleted since European discovery of the islands in the 16th Century, with populations declining from an estimated 250 000 to between 8000 and 14 000 in the 1970s. Successful tortoise conservation efforts have focused on species recovery, but ecosystem conservation and restoration requires a better understanding of the wider ecological consequences of this drastic reduction in the archipelago's only large native herbivore. We report the first evidence from palaeoecological records of coprophilous fungal spores of the formerly more extensive geographical range of giant tortoises in the highlands of Santa Cruz Island. Upland tortoise populations on Santa Cruz declined 500–700 years ago, likely the result of human impact or possible climatic change. Former freshwater wetlands, a now limited habitat‐type, were found to have converted to Sphagnum bogs concomitant with tortoise loss, subsequently leading to the decline of several now‐rare or extinct plant species.     

Movement Patterns of a Native and Non‐native Frugivore in Hawaii and Implications for Seed Dispersal

Avian frugivores historically played important roles as seed dispersers across the Hawaiian Islands, but presently, the ‘ōma‘o (Myadestes obscurus) is the only extant native frugivore in the wild on the Island of Hawaii. During recent decades, the introduced generalist Japanese White‐eye (Zosterops japonicus) has become the most common bird in Hawaii. The movements of avian frugivores largely dictate how far seeds get dispersed and into what kinds of microhabitats. This study compares the movement patterns and diet of the ‘ōma‘o to the Japanese White‐eye to understand how a native differs from a non‐native frugivore in the type and distances of seeds dispersed. Radiotelemetry was conducted on nine ‘ōma‘o and nine Japanese White‐eyes in a system of natural forest fragments (kīpuka) created by lava flows. Japanese White‐eyes disperse seeds approximately twice as far as ‘ōma‘o; during the time of gut passage, ‘ōma‘o move a mean distance of 98.1 m, and Japanese White‐eyes move 170.1–194.8 m. However, the ‘ōma‘o disperses the seeds of at least seven different native fruit species compared with two dispersed by Japanese White‐eyes. Japanese White‐eyes were found to disperse seeds smaller than 1.5 mm, whereas the ‘ōma‘o dispersed seeds up to 6 mm in diameter. Despite their ecological differences, both birds distribute certain seeds within and among kīpuka and likely facilitate primary succession of fruiting plants in the young lava matrix. However, this study suggests that if the ‘ōma‘o were extirpated, a smaller‐bodied generalist cannot entirely substitute for the ecological role played by the native frugivore.     

Conservation genetics of an island-endemic lizard: low Ne and the critical role of intermediate temperatures for genetic connectivity

Island populations are at higher risk of extinction than mainland populations. Therefore, understanding the factors that facilitate connectivity is particularly pressing for the conservation of island taxa. Sceloporus occidentalis becki, the Island Fence Lizard, is an endemic taxon restricted to the Northern Channel Islands, part of a nearshore archipelago in Southern California, USA. Since the Last Glacial Maximum, fence lizard habitat on the Northern Channel Islands has decreased with rising sea levels and increasing temperatures that have reduced the availability of woody vegetation. More recently, the introduction (and subsequent removal) of invasive ungulates over the last 170 years and recovery of vegetation has resulted in further dramatic habitat modification. Given the potential for genetic bottlenecks, the history of habitat alteration, and topographic and landscape complexity, we used landscape and population genetic approaches to characterize patterns of genetic diversity and structure of Island Fence Lizards on Santa Cruz Island, the largest of the Northern Channel Islands. Our analyses revealed shallow population structure across the island, low effective population size (N_e?=??~?200), and evidence for a recent genetic bottleneck. Landscape genetic analyses showed that connectivity is facilitated by tree canopy cover and shrubland, as well as by intermediate temperatures, emphasizing the importance of woody vegetation and habitats with variable thermal regimes as the climate warms. Combined, these population and landscape genetic analyses suggest that the Island Fence Lizard is of greater conservation concern than currently appreciated, and increased conservation management focus is warranted for this island endemic.

     

Offspring genetic structure reveals mating and nest infestation behaviour of an invasive parasitic fly (<Emphasis Type="Italic">Philornis downsi</Emphasis>) of Galápagos birds

The natural reproductive behaviour of invasive insects is pivotal knowledge for managing species of ecological or economic concern. We use microsatellites to examine female multiple mating and multiple nest infestations in the introduced parasitic fly, Philornis downsi, which causes high mortality in endemic birds on the Galápagos Islands. We analyse larvae and pupae within 57 nests from Santa Cruz and Floreana Islands in both the highland and lowland habitats. Sib-ship reconstructions of offspring revealed that up to five females may infest a single nest, while multiple mating in females was frequent (65% of reconstructed maternal genotypes), with an average of 1.91 (±0.06 SE) males per female. Genetic relatedness (R) of offspring within nests was generally low, though lowland nests on Floreana had higher R than highland nests. Knowledge of the reproductive behaviour of P. downsi is necessary for modelling appropriate management strategies, in particular, the sterile insect technique, for which success is greatly influenced by female multiple mating.     

Habitat association and coexistence of endemic and introduced ant species in the Galápagos Islands

1. We investigated ant communities in all main vegetation zones of the model island of Santa Cruz in the Galápagos archipelago (155 collection points, spread over 21 sites; 28 ant species collected), and evaluated the distribution, coexistence, and effect of environmental factors in a community composed of endemic, probably endemic, and introduced ants of the New World and exotic origin. 2. Introduced species were the most frequent, occurring in 98% of the samples, yet endemic and probably endemic species still occurred in 54% of the samples, and constituted one of three most common species. The present study revealed that the habitat type along with altitude and the tree cover are the primary factors shaping ant community composition. Little evidence was found for a competitively structured assemblage of ant species. 3. The present study confirmed the predominance of two dominant invasive species, Solenopsis geminata Fabricius and Wasmannia auropunctata Roger, whose abundances are negatively correlated. The abundance of S. geminata is positively correlated with the overall species richness, and with the proportion of other introduced species. The presence of both invasive ants is associated with a low evenness of ant communities. 4. The present study (i) stresses the dominance of introduced species and the relative resistance of endemic species, (ii) highlights the on‐going processes of species introductions and (iii) points out the need for adequate monitoring and conservation of the pristine and threatened environments that constitute the Galápagos Islands.     

Genetic analysis of the endemic island loggerhead shrike, <Emphasis Type="Italic">Lanius ludovicianus anthonyi</Emphasis>

Based on limited research, the island loggerhead shrike, Lanius ludovicianus anthonyi has been considered a distinct subspecies endemic to the northern California Channel Islands. We used mtDNA control region sequences and microsatellite genotyping to compare loggerhead shrikes from the southern California mainland (L. l. gambeli), San Clemente Island (L. l. mearnsi), and the northern islands (L. l. anthonyi). Habitats on the islands are recovering due to the removal of non-native ungulates on the islands, but may be transitioning to habitats less supportive of loggerhead shrikes, so this evaluation comes at a critical time. We utilized 96 museum specimens that were collected over a century to evaluate both spatial and temporal genetic patterns. Analysis of multilocus microsatellite genotypes indicated that historical specimens of loggerhead shrikes (collected between 1897 and 1986) from the two northern islands of Santa Rosa and Santa Cruz are genetically distinct from adjacent mainland and island shrikes. Birds from Santa Catalina Island showed mixed ancestry and did not cluster with the northern island birds. Historical specimens of L. l. mearnsi from San Clemente Island also showed mixed ancestry. Our study provides evidence that a genetically distinct form of loggerhead shrikes, L. l. anthonyi, occurred on the islands of Santa Rosa and Santa Cruz.     

Mass production of SNP markers in a nonmodel passerine bird through RAD sequencing and contig mapping to the zebra finch genome

Here, we present an adaptation of restriction‐site‐associated DNA sequencing (RAD‐seq) to the Illumina HiSeq2000 technology that we used to produce SNP markers in very large quantities at low cost per unit in the Réunion grey white‐eye (Zosterops borbonicus), a nonmodel passerine bird species with no reference genome. We sequenced a set of six pools of 18–25 individuals using a single sequencing lane. This allowed us to build around 600 000 contigs, among which at least 386 000 could be mapped to the zebra finch (Taeniopygia guttata) genome. This yielded more than 80 000 SNPs that could be mapped unambiguously and are evenly distributed across the genome. Thus, our approach provides a good illustration of the high potential of paired‐end RAD sequencing of pooled DNA samples combined with comparative assembly to the zebra finch genome to build large contigs and characterize vast numbers of informative SNPs in nonmodel passerine bird species in a very efficient and cost‐effective way.     

A genomewide catalogue of single nucleotide polymorphisms in white‐beaked and Atlantic white‐sided dolphins

The field of population genetics is rapidly moving into population genomics as the quantity of data generated by high‐throughput sequencing platforms increases. In this study, we used restriction‐site‐associated DNA sequencing (RADSeq) to recover genomewide genotypes from 70 white‐beaked (Lagenorhynchus albirostris) and 43 Atlantic white‐sided dolphins (L. acutus) gathered throughout their north‐east Atlantic distribution range. Both species are at a high risk of being negatively affected by climate change. Here, we provide a resource of 38 240 RAD‐tags and 52 981 nuclear SNPs shared between both species. We have estimated overall higher levels of nucleotide diversity in white‐sided (π = 0.0492 ± 0.0006%) than in white‐beaked dolphins (π = 0.0300 ± 0.0004%). White‐sided dolphins sampled in the Faroe Islands, belonging to two pods (N = 7 and N = 11), showed similar levels of diversity (π = 0.0317 ± 0.0007% and 0.0267 ± 0.0006%, respectively) compared to unrelated individuals of the same species sampled elsewhere (e.g. π = 0.0285 ± 0.0007% for 11 Scottish individuals). No evidence of higher levels of kinship within pods can be derived from our analyses. When identifying the most likely number of genetic clusters among our sample set, we obtained an estimate of two to four clusters, corresponding to both species and possibly, two further clusters within each species. A higher diversity and lower population structuring was encountered in white‐sided dolphins from the north‐east Atlantic, in line with their preference for pelagic waters, as opposed to white‐beaked dolphins that have a more patchy distribution, mainly across continental shelves.     

Monitoring the effects of <Emphasis Type="Italic">Rodolia cardinalis</Emphasis> on <Emphasis Type="Italic">Icerya purchasi</Emphasis> populations on the Galapagos Islands

In January 2002, the first biological control program was implemented on the Galapagos Islands with the release of the Australian coccinellid Rodolia cardinalis Mulsant to control the invasive cottony cushion scale, Icerya purchasi Maskell. This was the first time that Galapagos authorities had approved the introduction of a biological control agent to this iconic archipelago and, because of this precedent, it was important to monitor and evaluate its behaviour soon after its introduction. Surveys were carried out after the release of R. cardinalis in 2002 to confirm establishment on Santa Cruz Island. In 2009, seven years post-release, a broader survey was done to document spread throughout the archipelago. Directly after the release of R. cardinalis in 2002, a predator exclusion study and field observations were carried out on scale insect populations on white mangrove (Laguncularia racemosa [L.] Gaertn. F.) on Santa Cruz Island to document impact. In less than three months after R. cardinalis was released in 2002, populations of I. purchasi on white mangrove that were exposed to the predator in the exclusion experiment, or were monitored in the field, had declined by 99–100%. Results suggest that R. cardinalis played a key role in this decline, possibly in combination with high rainfall. Rodolia cardinalis dispersed quickly after its release and by 2009 was found in a wide variety of habitats on seven of the eight islands surveyed that had records of I. purchasi. Two of these were self-introductions. Further monitoring is recommended to determine whether this biological control agent has successfully reduced scale insect numbers on other valued plant species.     

Patterns of contact call differentiation in the panmictic East African Abyssinian White‐eye Zosterops abyssinicus (Aves: Passeriformes)

Species distribution patterns range from highly disjunct to continuous, depending on their ecological demands and the availability of respective habitats. East African savannahs are mostly interconnected and ecologically comparatively homogenous and thus provide a prerequisite for a rather panmictic distribution pattern for species occurring in this habitat. The Abyssinian white‐eye Zosterops abyssinicus is a savannah inhabiting bird species, representing such a continuous distribution. This species occurs in high abundances and is very mobile, and past population genetic studies have suggested that gene flow is high and genetic differentiation is low even across relatively large geographic distances. Further, only little morphological differences were found. In order to test for potential divergence in acoustic traits despite its interconnected geographic distribution, we analyzed 2795 contact calls of Z. abyssinicus, which were recorded at 19 sites across Kenya. Our data indicate weak, but significant differentiation in call characteristics across latitudinal gradients. We found strong changes in call characteristics in populations where Z. abyssinicus occurs in sympatry with its highland congener, Zosterops poliogaster. However, the changes in call characteristics in sympatry were in different directions and lead to strong differentiation of the sympatric populations to other conspecific populations potentially representing a case of cascade reinforcement. The detected spatial gradients likely result from ecological differences and balancing effects of natural and sexual selection.     

Origin and hidden diversity within the poorly known Galápagos snake radiation (Serpentes: Dipsadidae)

Galápagos snakes are among the least studied terrestrial vertebrates of the Archipelago. Here, we provide a phylogenetic analysis and a time calibrated tree for the group, based on a sampling of the major populations known to occur in the Archipelago. Our study revealed the presence of two previously unknown species from Santiago and Rábida Islands, and one from Tortuga, Isabela, and Fernandina. We also recognize six additional species of Pseudalsophis in the Galápagos Archipelago (Pseudalsophis biserialis from San Cristobal, Floreana and adjacent islets; Pseudalsophis hoodensis from Española and adjacent islets; Pseudalsophis dorsalis from Santa Cruz, Baltra, Santa Fé, and adjacent islets; Pseudalsophis occidentalis from Fernandina, Isabela, and Tortuga; Pseudalsophis slevini from Pinzon, and Pseudalsophis steindachneri from Baltra, Santa Cruz and adjacent islets). Our time calibrated tree suggests that the genus Pseudalsophis colonized the Galápagos Archipelago through a single event of oceanic dispersion from the coast of South America that occurred at approximately between 6.9?Ma and 4.4?Ma, near the Miocene/Pliocene boundary.www.zoobank.org/urn:lsid:zoobank.org:pub:2679FD19-01E5-48FE-A0DA-A88FF145DE56     

Systematics,biogeography and evolution of the endemic Hemidactylus geckos (Reptilia,Squamata, Gekkonidae) of the Cape Verde Islands: based on morphology and mitochondrial and nuclear DNA sequences

A total of 1854 bp of mitochondrial DNA (669 bp of cytochrome b (cyt b) and 386 bp of 12S rRNA), and 804 bp of a nuclear gene (RAG2) were investigated in endemic Hemidactylus from eight Cape Verde Islands, and used to explore their phylogeny, biogeography and evolution. Maximum‐likelihood, maximum‐parsimony and Bayesian analyses based on mtDNA revealed four well‐supported clades with uncorrected genetic divergences of 7.8–12.4% in the cyt b plus 12S rRNA genes, which were also supported by nuclear DNA. A population from the southern island of Fogo is the most divergent in both molecules and morphology and is described as Hemidactylus lopezjuradoi sp. n., and the populations on Sal and Boavista are also assigned species status as H. boavistensis. Although divergent in their DNA, the clade on S. Nicolau and that in the north‐western islands are morphologically similar and both are assigned to H. bouvieri for the present. Hemidactylus b. razoensis from Raso is genetically similar to H. b. bouvieri and differs only in its smaller body size. A molecular clock suggests that the ancestor of the endemic Hemidactylus of the Cape Verde Islands colonized the archipelago approximately 10 ± 2.48 Mya, perhaps reaching the north‐eastern islands first. The H. lopezjuradoi lineage separated soon after, and the north‐western islands were colonized progressively but slowly, S. Nicolau probably being reached first, then S. Vicente and islands on the same bank, and finally Sto. Antão, which is likely to have been colonized less than 1 Mya. Hemidactylus boavistensis is abundant on the arid islands where it occurs, but H. bouvieri appears to have been uncommon at least since it was described 130 years ago, and the same may be true of H. lopezjuradoi sp. n. The impact of introduced H. angulatus and H. mabouia on the endemic Hemidactylus of the Cape Verde Islands is not clear, but the discovery of substantial genetic diversity in endemic Cape Verde Hemidactylus means that the conservation requirements of the group should be reassessed.     

White‐tailed deer as the last megafauna dispersing seeds in Neotropical dry forests: the role of fruit and seed traits

Endozoochory is a prominent form of seed dispersal in tropical dry forests. Most extant megafauna that perform such seed dispersal are ungulates, which can also be seed predators. White‐tailed deer (Odocoileus virginianus) is one of the last extant megafauna of Neotropical dry forests, but whether it serves as a legitimate seed disperser is poorly understood. We studied seed dispersal patterns and germination after white‐tailed deer gut passage in a tropical dry forest in southwest Ecuador. Over 23 mo, we recorded ca 2000 seeds of 11 species in 385 fecal samples. Most seeds belonged to four species of Fabaceae: Chloroleucon mangense, Senna mollissima, Piptadenia flava, and Caesalpinia glabrata. Seeds from eight of the 11 species dispersed by white‐tailed deer germinated under controlled conditions. Ingestion did not affect germination of C. mangense and S. mollissima, whereas C. glabrata showed reduced germination. Nevertheless, the removal of fruit pulp resulting from ingestion by white‐tailed deer could have a deinhibition effect on germination due to seed release. Thus, white‐tailed deer play an important role as legitimate seed dispersers of woody species formerly considered autochorous. Our results suggest that more research is needed to fully understand the ecological and evolutionary effects of the remaining extant megafauna on plant regeneration dynamics in the dry Neotropics.     

Microsatellite loci for the critically endangered Santa Cruz long-toed salamander (Ambystoma macrodactylum croceum) and other Ambystoma taxa

The imperiled Santa Cruz long-toed salamander (Ambystoma macrodactylum croceum) is a geographically isolated lineage of the long-toed salamander species complex. Recovery of this taxon requires understanding its population genetic structure, which is necessary to identify critical habitat. To assess the population structure of A. m. croceum, I developed primers for 17 microsatellite loci and evaluated their performance. Polymorphism ranged from 3 to 10 alleles per locus, with an average of 6.3 per locus. Mean observed and expected heterozygosity were similar (H _O = 0.678; H _E = 0.708), with one locus demonstrating heterozygote deficiency. The performance of these and previously identified microsatellite loci were also characterized for two other long-toed salamander lineages, as well as two other species of Ambystoma. The utility of these markers has similar and overlapping applications for conservation and population genetics studies of other Ambystoma taxa, and will provide a basis for revising the recovery plan for A. m. croceum, particularly for designating corridors among interacting breeding populations and upland areas, and identifying areas where gene flow should be restored.     

Patterns of bird species richness and composition on islands off Arnhem Land,Northern Territory,Australia

The bird faunas of the adjacent Wessel and English Company island chains were sampled at two scales (0.25 ha quadrats and entire islands). Ninety‐six species were recorded from 226 quadrats, with the most frequently recorded species being mistletoebird Dicaeum hirundinaceum, brown honeyeater Lichmera indistincta, silver‐crowned friarbird Philemon argenticeps, bar‐shouldered dove Geopelia humeralis, northern fantail Rhipidura rufiventris and yellow white‐eye Zosterops lutea. At the quadrat scale, vegetation type was a major determinant of the abundance of individual species (and hence species composition), species richness and total bird abundance. Bird species composition and richness at the quadrat scale was also significantly affected by island isolation (particularly the amount of land within 20 km of the island perimeter). Island size had no effect on quadrat‐scale richness or total abundance. However, the abundance of 10 of the 38 most frequently recorded individual species was significantly related to island size, in most cases even when the comparison was restricted to similar habitats. The most striking cases were rufous fantail Rhipidura rufifrons, mangrove golden whistler Pachycephala melanura, brown honeyeater and yellow white‐eye, which were all significantly more abundant on smaller islands. One hundred and seventy‐one species were recorded from the 62 islands sampled. There was a very tight relationship between island size and the number of terrestrial species (73% of deviance explained) and of all species (84% of deviance explained). This relationship was improved (marginally) when isolation was included in the model. Ordination of islands by their terrestrial bird species composition was related to island size and isolation, and suggested an erratic species composition on small islands.     

The population genetics of nonmigratory Allen’s Hummingbird (Selasphorus sasin sedentarius) following a recent mainland colonization

Allen''s Hummingbird comprises two subspecies, one migratory (Selasphorus sasin sasin) and one nonmigratory (S. s. sedentarius). The nonmigratory subspecies, previously endemic to the California Channel Islands, apparently colonized the California mainland on the Palos Verdes Peninsula some time before 1970 and now breeds throughout coastal southern California. We sequenced and compared populations of mainland nonmigratory Allen''s Hummingbird to Channel Island populations from Santa Catalina, San Clemente, and Santa Cruz Island. We found no evidence of founder effects on the mainland population. Values of nucleotide diversity on the mainland were higher than on the Channel Islands. There were low levels of divergence between the Channel Islands and the mainland, and Santa Cruz Island was the most genetically distinct. Ecological niche models showed that rainfall and temperature variables on the Channel Islands are similar in the Los Angeles basin and predicted continued expansion of nonmigratory Allen''s Hummingbird north along the coast and inland. We also reviewed previous genetic studies of vertebrate species found on the Channel Islands and mainland and showed that broad conclusions regarding island–mainland patterns remain elusive. Challenges include the idiosyncratic nature of colonization itself as well as the lack of a comprehensive approach that incorporates similar markers and sampling strategies across taxa, which, within the context of a comparative study of island–mainland relationships, may lead to inconsistent results.     

Notes on the Poaceae of the Robinson Crusoe (Juan Fernández) Islands, Chile

Notes on the Poaceae of the Robinson Crusoe (Juan Fernández) Islands, Chile, Brittonia 54: 154–163. 2001.—Poaceae in the Robinson Crusoe (=Juan Fernández) Islands number 53 species in 32 genera, of which 9% of the species are endemic, 9% indigenous, and 81% adventitious. The endemic taxa (and their conservation status) are:Agrostis masafuerana (rare),Chusquea fernandeziana (not endangered),Megalachne berteroana (not endangered),M. masafuerana (not endangered), andPodophorus bromoides (extinct).Megalachne andPodophorus are endemic genera. Comparisons with Poaceae in the Bonin and Volcano Islands, Canary Islands, Galápagos Islands, and Hawaiian Islands show different levels of endemism: number of endemic taxa, respectively, 5, 10, 12, 40; percent specific endemism, 8, 6, 21, 19. No endemic genera occur.Anthoxanthum odoratum, Avena barbata andHordeum murinum are noxious weeds in the Robinson Crusoe Islands. Many adventives are shared among floras of the archipelagos, with the highest ties of Robinson Crusoe being to the Canaries (53% of total Poaceae known in Juan Fernández) and the Hawaiian Islands (47%). Low levels of adventives occur within the Bonin (5%) and Galápagos (7%) Islands. In contrast, there are many endemic genera of Asteraceae in these same archipelagos: Bonin and Volcano Islands (1), Canary Islands (8), Galápagos Islands (5), and Hawaiian Islands (6); percent of specific endemism is also higher (20, 53, 54 and 56, respectively). Hypotheses for greater levels of endemics among oceanic island Asteraceae include more efficient dispersal mechanisms by wind and birds, animal pollination systems that result in greater degrees of geographic populational genetic isolation, and a vascular cambium that offers enhanced growth-form evolutionary opportunities.     

Conservation implications of high genetic variation in two closely related and highly threatened species of Crambe (Brassicaceae) endemic to the island of Gran Canaria: C. tamadabensis and C. pritzelii

We used data from 12 allozyme loci for two endemic Brassicaceae from Gran Canaria (the endangered narrow endemic Crambe tamadabensis and its more widespread congener C. pritzelii) to assess whether their genetic diversity patterns reflect their phylogenetic closeness and contrasting population sizes and distribution areas, and to derive conservation implications. Genetic diversity values are high for both species and slightly higher in C. tamadabensis, despite its narrow distribution in north‐western Gran Canaria. At odds with the generally high interpopulation diversity levels reported in Canarian endemics, values of G_ST in C. tamadabensis and C. pritzelii are rather low (0.067 and 0.126, respectively). We construe that the higher genetic structure detected in C. pritzelii is mainly a result of unbalanced allele frequencies and low population sizes at the edges of its distribution. The overall high allozyme variation detected in C. tamadabensis and C. pritzelii is nevertheless compatible with an incipient but consistent genetic differentiation between the two species, modulated by recurrent bottlenecks caused by grazing and drift. Our data suggest that conservation efforts aimed at maintaining the existing genetic connectivity in each species and ex situ conservation of seeds are the best strategies to conserve their genetic diversity.