Population structure and intraspecific aggression in the invasive ant species Anoplolepis gracilipes in Malaysian Borneo

Invasive species are one of the main sources of the ongoing global loss of biodiversity. Invasive ants are known as particularly damaging invaders and their introductions are often accompanied by population-level behavioural and genetic changes that may contribute to their success. Anoplolepis gracilipes is an invasive ant that has just recently received increased attention due to its negative impact on native ecosystems. We examined the behaviour and population structure of A. gracilipes in Sabah, Malaysia. A total of 475 individuals from 24 colonies were genotyped with eight microsatellite markers. Intracolonial relatedness was high, ranging from 0.37 to 1 (mean +/- SD: 0.82 +/- 0.04), while intercolonial relatedness was low (0.0 +/- 0.02, range -0.5-0.76). We compared five distinct sampling regions in Sabah and Brunei. A three-level hierarchical F-analysis revealed high genetic differentiation among colonies within the same region, but low genetic differentiation within colonies or across regions. Overall levels of heterozygosity were unusually high (mean H(O) = 0.95, mean H(E) = 0.71) with two loci being entirely heterozygous, indicating an unusual reproductive system in this species. Bioassays revealed a negative correlation between relatedness and aggression, suggesting kinship as one factor facilitating supercolony formation in this species. Furthermore, we genotyped one individual per nest from Sabah (22 nests), Sarawak (one nest), Brunei (three nests) and the Philippines (two nests) using two mitochondrial DNA markers. We found six haplotypes, two of which included 82.1% of all sequences. Our study shows that the sampled area in Sabah consists of a mosaic of differently interrelated nests in different stages of colony establishment. While some of the sampled colonies may belong to large supercolonies, others are more likely to represent recently introduced or dispersed propagules that are just beginning to expand.     

Spatial dynamics of supercolonies of the invasive yellow crazy ant, Anoplolepis gracilipes, on Christmas Island, Indian Ocean

Key to the management of invasive species is an understanding of the scope of an invasion, the rate of proliferation and the rate at which invaded habitats become degraded. This study examines the spatial dynamics of high-density supercolonies of the invasive yellow crazy ant, Anoplolepis gracilipes , on Christmas Island, Indian Ocean, and the associated impacts at their boundaries. Since the early 1990s, A. gracilipes supercolonies have occupied over 30% of the 10,000 ha of rainforest on Christmas Island. Thirty-four discrete high-density supercolonies formed between 1989 and 2003, ranging in size across nearly three orders of magnitude from 0.9 to 787 ha. Supercolonies boundaries are diffuse, and ants were observed in low densities in some cases up to 200 m from the main high-density supercolony. The 13 boundaries examined were all dynamic over a 10–20 observation month period: nine boundaries expanded, and the maximum rate of spread was 0.5 m day⁻¹. Across boundary transition zones, between high-density supercolonies and intact rainforest, yellow crazy ants reduced other ant species richness, occupied red crab burrows and killed resident red crabs, which was the trigger for 'invasional meltdown' on Christmas Island. The highly variable and unpredictable nature of A. gracilipes boundaries poses a challenge for incorporation into a predictive framework, as well as for their management.     

Impact of the invasive crazy ant Anoplolepis gracilipes on Bird Island, Seychelles

The crazy ant (Anoplolepis gracilipes) invaded Bird island, Seychelles, in the 1980s. In 1997, its range expanded and population densities increased. The impacts of this change were studied in 2001 using a combination of arthropod collecting methods. The ant population excluded larger invertebrates (principally the large ant Odontomachus simillimus and the crabs, principally Ocypode spp.). Cockroaches, however, remained abundant in ant-infested areas and tree-nesting birds (Lesser Noddy Anous tenuirostris) appear to be able to breed successfully in the presence of the crazy ant. The ants are only abundant in areas of deep shade which provide cool nesting areas, yet enabling them to forage in the open when ground temperatures fall. The expansion of the ants was correlated with the regeneration of woodland on the island. Recommendations are made for the management of the woodland which may reduce the impacts of the crazy ant.     

Supercolonies of the invasive yellow crazy ant, Anoplolepis gracilipes, on an oceanic island: Forager activity patterns, density and biomass

Summary. Ants have the capacity to reach unusually high densities, mostly in their introduced ranges. Numerical dominance is often cited as key to the ability of exotic ants to displace native ant species, reduce the abundance of invertebrates and negatively impact upon bird, land crab and other vertebrate populations. On Christmas Island, Indian Ocean, the yellow crazy ant, Anoplolepis gracilipes (Jerdon), forms supercolonies, where extremely high densities of foraging ants have contributed to ‘invasional meltdown’ in rainforest areas. Densities of up to 2254 foraging ants per m² and a biomass of 1.85 g per m² were recorded, and nest densities reached 10.5 nest entrances per m². Populations of A. gracilipes can overcome and kill red endemic land crabs (Gecarcoidea natalis) over 100 times their own biomass. This is the highest recorded density of foraging ants, and adds another element to the definition of ‘supercolony’ of unicolonial ants. This paper documents one extreme in a continuum of densities of unicolonial, invasive ant species and highlights the need to incorporate forager densities into invasive ant research.Received 17 November 2004; revised 14 February 2005, accepted 21 February 2005.     

Isolation and characterization of microsatellite loci from the invasive ant Pheidole megacephala

We report the characterization of eight microsatellite markers in the big-headed ant Pheidole megacephala, a pest ant registered in the list of '100 of the world's worst invasive alien species'. An enrichment protocol was used to isolate microsatellite loci, and polymorphism was explored with 36 individuals collected in an invasive population from Australia and 20 individuals collected in a population from the native mainland location in South Africa. These primers showed a number of alleles per locus ranging from two to 10, and expected heterozygosities ranging from 0.083 to 0.826. Moreover, results of cross-species amplification are reported in five other Pheidole species and in seven other ants of the subfamily Myrmicinae.     

Impact of the introduced yellow crazy ant Anoplolepis gracilipes on Bird Island, Seychelles

The introduced yellow crazy ant or long-legged ant Anoplolepis gracilipes was first reported in Seychelles in 1969 and now occurs on at least nine islands in the Central Seychelles. We describe the yellow crazy ant's effects on vegetation and invertebrate communities on one of these, Bird Island; in 2000, Anoplolepis (first reported in 1991) occurred there at densities at least 80 times higher than on other islands in the Central Seychelles. They were associated with high densities of coccid scale insects on foliage, especially of the native tree Pisonia grandis, in some instances causing tree death. Yellow crazy ants on Bird Island also significantly affected invertebrate communities on foliage and on the ground, both in terms of taxonomic composition and the density of specific taxa, apparently causing the local exclusion of some invertebrates.     

西双版纳入侵长足捷蚁与土著黄猄蚁的种间竞争

【目的】入侵物种能够通过竞争影响本地物种的种群,从而影响入侵地的生物多样性。长足光捷蚁Anoplolepis gracilipes是全球最具破坏力的入侵蚂蚁之一。本研究旨在明确西双版纳地区入侵长足捷蚁与土著优势种蚂蚁黄猄蚁Oecophylla smaragdina之间的竞争关系。【方法】通过野外调查和室内控制试验相结合的方法,观察和对比分析长足捷蚁和黄猄蚁的体型大小,雾凉季和雨季的巢穴外觅食活动规律,觅食能力(搜寻食物的时间、在觅食时间内召集的最大工蚁数),打斗行为(不同打斗组合的攻击强度和死亡率)以及对饥渴的耐受性(无食物和水分供应时平均存活时间和存活率随时间的变化)。【结果】长足捷蚁工蚁体长(3.66±0.06 mm)显著小于黄猄蚁工蚁(8.27±0.16 mm)。在雾凉季时,长足捷蚁具有比黄猄蚁更长的觅食活动时间;而在雨季时,两种蚂蚁均在下午温度较高时段觅食活动的个体数量减少。苹果、蜂蜜和火腿肠3种食物作为诱饵时,长足捷蚁具有更快搜寻食物的能力,4~8 min便能找寻到食物,而黄猄蚁需要8~21 min才能找寻到食物,此外在寻找到食物后,长足捷蚁也有更快召集同伴的能力。在人工控制试验中,1头长足捷蚁和1头黄猄蚁同时存在时主要以不攻击和低强度攻击为主,而当两种蚂蚁中的任意其中一种的个体数量增加到5头时,攻击强度会显著增加,两种蚂蚁均存在种间协作行为。在饥渴状态下,两种蚂蚁工蚁的平均存活时间差异不显著,但长足捷蚁最长存活120 h,黄猄蚁最长存活96 h。【结论】在西双版纳地区,长足捷蚁相较于土著黄猄蚁具有更强的觅食的能力,雾凉季觅食活动时间更长,暗示长足捷蚁可能具有较强的温度适应能力。有必要加强对这一入侵蚂蚁的研究,并密切关注其种群在该地区的发展。     

Characterization of polymorphic microsatellite loci for the invasive monk parakeet (Myiopsitta monachus)

Microsatellite loci were characterized for the monk parakeet (Myiopsitta monachus) from a GT_n‐enriched genomic library. Twelve of 14 microsatellite loci were polymorphic, averaging 6.7 alleles per locus across the 20 individuals genotyped. Mean expected heterozygosity was 0.72, with locus‐specific values ranging from 0.53 to 0.90. An equally high multilocus probability of identity (2.48 × 10^?12) was revealed for this set of loci. In addition, all 12 loci were demonstrated to cross‐amplify to varying extents within three additional parrot genera suggesting their potential utility for population‐level studies in a broad range of Neotropical psittacines.     

Isolation and characterization of nine microsatellite markers for Brachypodium sylvaticum (Huds.) Beauv., a recently invasive grass species in Oregon

The patterns of genetic diversity caused by rapid range expansions following recent colonizations are best observed using highly polymorphic genetic markers. We characterized nine microsatellite markers for Brachypodium sylvaticum, a bunchgrass invasive in the Northwestern United States and native to Eurasia. Loci exhibited from two to 10 alleles, and generally had high F(IS) values. These loci will help identify sources of new populations in the region, and they will be useful for studying patterns of genetic diversity during rapid range expansions.     

美国对入侵种的管理对策

外来种入侵是产生当前世界生物多样性危机的重要原因之一。目前外来种入侵问题已经引起人们的普遍关注。1999年2月美国联邦政府发布总统令,号召联邦政府机构执行人员防止外来入侵种所造成的严重环境威胁,指示有关职能部门行使职权阻止引入入侵种并且恢复本地种。总统令指示建立一个入侵物种理事会,并就理事会、联邦机构的职责做了相应界定。美国农业部等部门支持的入侵植物管理国家策略项目,提出了针对入侵种的三项国家目标一入侵种的预防、控制和本地种的恢复。国家管理策略的制定不同层次的人们提供了合作、教育和研究的机遇。美国政府部门以及有关社会团体已经就外来种入侵危害防范积极展开行动,包括制定标准防止入侵种进入,控制、根除入侵种,向民众进行有关外来种入侵的教育,增加财政年度预算等等。     

外来种入侵的生物学与生态学基础的若干问题

外来物种的入侵及其所造成的危害已越来越为人们所认识。一个外来物种入侵一个新的生境无疑要具备一定的条件 ,尽管目前对这种条件的研究还只是初步的。首先从其自身来说 ,需要有足够的入侵性 ,这可以认为是入侵种的生物学基础 ,可能表现为具有多倍性、一定的遗传变异、杂合性或表型可塑性 ,以及不同的交配系统等 ;其次一个物种的入侵成功还取决于入侵生境的可入侵性 ,这可以认为是入侵种的生态学基础 ,而新的种间关系的形成 ,尤其是入侵种与其他种类的互惠共生关系的建成是关键。本文主要介绍了有关入侵种的生物学和生态学基础中的一些最新进展 ,希望有助于我国学者对相关研究内容的开展以及对有害外来种入侵的防治     

Development and characterization of microsatellite markers for the invasive weed Mikania micrantha (Asteraceae)

Mikania micrantha is a successful invasive weed in many parts of the world. Twelve polymorphic microsatellite loci were isolated and characterized from an AC-enriched genomic library of this species. Twenty-eight individuals from one population in Dongguan were tested for polymorphism. The average allele number of these microsatellites was three per locus, ranging from two to five. The expected and observed heterozygosities ranged from 0.275 to 0.742, and from 0.250 to 1.000, respectively. These microsatellite markers can be applied to study the population genetics in the native and invasive ranges of this species, and to trace its invasion history.     

Characterization of novel microsatellite markers for Eschscholzia californica (Papaveraceae), an invasive species in central Chile

? Premise of the study: We isolated and characterized microsatellite markers for the California poppy, Eschscholzia californica, which is an invasive species in central Chile. ? Methods and Results: A total of eight polymorphic and six monomorphic loci were developed for the species. Between one and 12 alleles were observed per locus. Polymorphic loci showed heterozygosity ranging from 0 to 0.875 in a sample of 96 individuals obtained from four populations. Only one locus showed significant departures from Hardy-Weinberg equilibrium at all sites. ? Conclusions: The successful microsatellite amplification makes this set of primers an important tool for understanding the recent and future patterns of invasion and adaptation of E. californica into the new Chilean geographic area. The variation detected is currently being used in a more inclusive study that assesses population expansion in central Chile.     

Characterization of microsatellite markers for Sycoscapter nonpollinating fig wasps

We isolated 18 microsatellites from Sycoscapter australis, a nonpollinating fig wasp that develops in figs of Ficus macrophylla, and assessed their variability in 20 wasps. We further optimized nine of these loci for use in three other Sycoscapter species that develop in Ficus rubiginosa figs and assessed their variability in 47-140 wasps per species. These are the first microsatellites developed for nonpollinating fig wasps and show sufficient polymorphism to become important tools in evolutionary and genetical studies of Sycoscapter wasps.     

Interference and exploitation competition of three nectar-thieving invasive ant species

Summary. Plant and insect exudates are known to play a key role in structuring tropical ant communities, but less is known about the utilization of these resources in communities dominated by invasive ants. Invasive ants are thought to require large amounts of carbohydrates such as honeydew or nectar to maintain their high abundances. Invasive ants that consume floral nectar may compete with legitimate floral visitors through interference or exploitation competition. I compared the nectar-thieving behavior of three widespread invasive ant species: long-legged ants (Anoplolepis gracilipes), Argentine ants (Linepithema humile), and big-headed ants (Pheidole megacephala) in inflorescences of the native Hawaiian ‘ōhi’a tree, an important food source for native fauna. A. gracilipes was least likely to leave inflorescences unvisited and visited inflorescences in higher numbers than both L. humile and P. megacephala. A. gracilipes and L. humile visited more flowers in an inflorescence and were less likely to retreat from a flower with a competitor than P. megacephala. A. gracilipes was able to take 5.5 and 11.3 times the amount of nectar than L. humile and P. megacephala, respectively. Thus, A. gracilipes may be effective at both interference and exploitation competition against other nectarivores, L. humile may be effective at interference competition, and P. megacephala may be relatively weak at both types of competition against other nectarivores. Ascertaining the competitive abilities of invasive ants against legitimate floral visitors will be especially important in agricultural and other systems that are nectar or pollinator limited.Received 6 December 2004; revised 13 January 2005; accepted 14 January 2005.     

The conundrum of the yellow crazy ant (Anoplolepis gracilipes) reproductive mode: no evidence for dependent lineage genetic caste determination

Asexual reproduction and hybridisation are often found among highly invasive plants and marine invertebrates. Recently, it has been suggested that clonality may enhance the success of invasive ants. In contrast, obligate hybridisation (dependent lineage genetic caste determination or DL GCD in ants) may decrease the chances of population persistence if one lineage is less prevalent than the other (asymmetry in lineage ratio). Genetic data available for the invasive yellow crazy ant (Anoplolepis gracilipes) suggest that it has an unconventional mode of reproduction that may involve asexual reproduction by workers or queens, or a form of genetic caste determination. Here, we investigated whether A. gracilipes reproduction involved DL GCD. The potential for worker reproduction was also assessed. We used microsatellite markers to assess the population structure of A. gracilipes workers, males, queens and sperm in queen spermathecae, from field collections in Arnhem Land. We found that a single queen lineage is present in Arnhem Land. The presence of a single lineage of queens discounts the possibility of DL GCD. Population structure separated queens and workers into different lineages, suggesting that these castes are determined genetically in A. gracilipes, or the mode of reproduction differs between workers and queens. Evidence for worker reproduction was weak. We conclude that the reproductive mode of A. gracilipes does not involve DL GCD. The resolution of the reproductive mode of A. gracilipes is complicated by a high prevalence of diploid males. The determination of the A. gracilipes reproductive mode remains a fascinating research question, and its resolution will improve our understanding of the contribution of the reproductive system to invasion success.     

Community level impacts of an ant invader and food mediated coexistence

Ant invasions exert a range of effects on recipient communities, from displacement of particular species to more complex community disruption. While species loss has been recorded for a number of invasion events, a little examined aspect of these invasions is the mechanisms for coexistence with resident ant species.The yellow crazy ant, Anoplolepis gracilipes (Smith), is considered one of the world’s worst ant invaders and has recently undergone rapid population growth in Tokelau. We surveyed the ground-dwelling ant fauna in two plots on each of five invaded and three uninvaded islands across two atolls in Tokelau to examine community characteristics of the ant fauna in areas with and without yellow crazy ants. We also used three types of food bait (tuna, jam and peanut butter) to experimentally test if species are able to coexist by consuming different food resources. Anoplolepis gracilipes was found to coexist with two to six other ant species at any one site, and coexisted with a total of 11 ant species. Four species never co-occurred with A. gracilipes. Non-metric multidimensional scaling showed significant differences in community composition and the relative abundance of species between areas that had, and had not, been invaded by A. gracilipes. The number of other ant species was significantly lower in communities invaded by the yellow crazy ant, but did not decline with increasing A. gracilipes abundance, indicating that impacts were independent of population density. The yellow crazy ant dominated all tuna and jam baits, but had a low attendance on peanut butter, allowing four other ant species to access this resource. Our results demonstrate community level impacts of an ant invader on a tropical oceanic atoll and suggest that differing use of food resources can facilitate coexistence in ant communities. Received 11 September 2006; revised 15 January 2007; accepted 22 February 2007.     

Characterization of microsatellite markers for rough fescue species (Festuca spp.)

One major challenge in genetic diversity analysis of minor grass species is the lack of informative molecular markers. A set of 210 simple sequence repeat (SSR) markers developed from wheat and barley were evaluated for their transferability to three rough fescue species [Festuca altaica Trinius, F. campestris (Rydb.) and F. hallii (Vassey) Piper]. Twelve SSR primer pairs displayed scorable polymorphism among and within the species. The number of alleles per primer pair ranged from three to 17 with an average of 8.3 for all the species and greatly varied for each species. About 82% of SSR variation resided within the species. Festuca hallii was genetically most distinct among the three species.