Counterattack success of a social spider mite against two predominant phytoseiid predator species

A survey was conducted of the predator fauna occurring in and around the nests of the two forms (LW: low male aggression and HG: high male aggression) of Stigmaeopsis miscanthi (Saito) that occur in Japan. Two phytoseiid species, Neoseiulus womersleyi (Schicha) and Typhlodromus bambusae Ehara predominated in S. miscanthi nests and their respective occurrence frequencies were the same in LW form nests as in HG form nests. We examined the counterattack success of S. miscanthi LW form males against these two phytoseiid predators. It was shown that while LW form male(s) could kill or effectively drive the larvae of both predator species out of their nests, there were no significant differences in the male counterattack success rate between 1-male and 2-male defended nests, or against the two predator species. On the other hand, there was a significant difference between the two predator species’ behavioral response to male-defended nests.     

Variation in counterattack effect against a phytoseiid predator between two forms of the social spider mite, <Emphasis Type="Italic">Stigmaeopsis miscanthi</Emphasis>

In Japan, Stigmaeopsis miscanthi (Saito) occurs in two forms that are differentiated by the intensity of male-to-male aggression, i.e. there is a low aggression and a high aggression group (known as the LW and HG forms, respectively). The effects of counterattack behavior against predators were experimentally compared between the two forms. Parental males and females of both forms could achieve significant counterattack success against Typhlodromus bambusae, a specific predator, and counterattack efficiency increased significantly with parental density. Furthermore, the HG form showed a stronger tendency than the LW form to kill predator larvae. Thus, variation in counterattack success may exist between these two forms, and there is some correspondence between male-to-male belligerence and counterattack effectiveness against predators.     

Asymmetry in male lethal fight between parapatric forms of a social spider mite

Closely related species often show adjacent geographic distributions, albeit with some overlap. This contiguity is thought to result from secondary contact between (spatially separated) diverging groups or from parapatric speciation. Fights between males of closely related species will affect their chance to mate with females of the other species, which in turn may promote their spatial segregation and drive their speciation. Stigmaeopsis miscanthi is a social spider mite that lives in a group within self-woven nests on leaves of Chinese silver grass. This mite shows lethal male–male fight as a means to maintain a harem, and has two forms showing differences in the levels of male–male aggression, diapause intensity in females and the relative length of the first to third legs. The two forms show parapatric distributions. We found that males of one form readily engage themselves in lethal fight with males of the other form, thereby acquiring the nests and gaining access to females of this other form. Males of the aggressive form tend to win the fights with males of the other form. Their first legs are longer which may provide them with a better weapon and which also indicate a larger body width. However, another determinant of who wins the fight is the length of the third legs which can be a proxy for body length. Based on these results, we hypothesize that male killing behavior is one of the mechanisms maintaining parapatry (instead of sympatry) of the two spider mite forms apart from difference in diapause attributes.     

Life history differences between two forms of the social spider mite, Stigmaeopsis miscanthi

The two forms of Stigmaeopsis miscanthi (Saito) (called LW and HG) differ in their levels of male-to-male aggression, differ in their diapause attributes, and morphologically in the male leg I armor. Furthermore, a type of reproductive isolation exists between the forms, although some one-way compatibility is maintained. Here we looked for any differences in life history traits between the two forms under experimental conditions. The intrinsic rate of natural increase (r _m ) of the LW form was lower than that of the HG form, the difference seemingly caused by the developmental speed of the latter. Although the developmental speeds of HG under several temperature regimens were significantly higher than those of LW, the low development threshold temperatures of the two forms were almost identical. This study addresses why a significant difference in r _m exists in relation to other behavior and physiological (diapause) adaptations.     

Male–male aggression peaks at intermediate relatedness in a social spider mite

Theory predicts that when individuals live in groups or colonies, male–male aggression peaks at intermediate levels of local average relatedness. Assuming that aggression is costly and directed toward nonrelatives and that competition for reproduction acts within the colony, benefits of aggressive behavior are maximized in colonies with a mix of related and unrelated competitors because aggression hurts nonkin often, thereby favoring reproduction of kin. This leads to a dome‐shaped relation between male–male aggression and average relatedness. This prediction has been tested with bacteria in the laboratory, but not with organisms in the field. We study how male–male aggression varies with relatedness in the social spider mite Stigmaeopsis miscanthi. We sampled 25 populations across a wide geographic range between Taiwan and Japan, representing a gradient of high to low within‐population relatedness. For each population the weaponry of males was measured as the length of the first pair of legs, and male–male aggression was tested by placing pairs of nonsibling males together and scoring the frequency of male death over a given period. As these two morphological and behavioral variables correlate strongly, they both reflect the intensity of male–male conflict. Our data on the social spider mite show that male–male aggression as well as weapon size strongly peak at intermediate, average relatedness, thereby confirming theoretical predictions.     

Correspondence of male-to-male aggression to spatial distribution of individuals in field populations of a subsocial spider mite

The intensity of male-to-male aggression, when evaluated in the laboratory, varies geographically in a subsocial spider mite, Schizotetranychus miscanthi Saito. This species includes two types of populations showing different clinal trends in aggression. We examined the relationships between the intensity of male aggression and the distribution patterns of individuals within nests for 22 field populations of the "low-aggression group." The intensity of male aggression was negatively correlated with the index of male aggregation across nests, which strongly suggests that aggression measured under experimental conditions is actually reflected in the interaction between males within nests in the field. The intensity of male aggression was also negatively correlated with the mean number of males per nest, suggesting that mortal fight between males, observed in the laboratory, actually occurs in the field. Received: October 14, 1999 / Accepted: May 22, 2000     

Differences in diapause attributes between two clinal forms distinguished by male-to-male aggression in a subsocial spider mite, Schizotetranychus miscanthi Saito

The nest-weaving spider mite Schizotetranychus miscanthi Saito showed a cline in male-to-male aggression intensity with minimum winter temperature. The altered kin structure in spring nests, which might be caused by winter harshness, was hypothesized to be a key factor responsible for the cline in male-to-male aggression. In Japan, we found two forms (high- and low-aggression forms) that showed different clinal trends with similar regression slopes and different intercepts. The former is characteristic of local populations from milder climates, whereas the latter occurs in harsher climates. We hypothesized that the intensity of female diapause, which may determine whether males are produced during late winter, was one of the factors separating these two clinal forms. In the four populations studied, short day length during the developmental period (egg to adult emergence) induced diapause in females. Diapause intensity varied greatly among populations, and particularly between the high-aggression and low-aggression forms. These data, together with data on winter harshness between the localities, led us to believe that female diapause is one of the factors affecting relatedness between interacting males in nests and can explain why the two forms of S.miscanthi have different clinal trends in male aggression in Japan.     

Postglacial range shift and demographic expansion of the marine intertidal snail Batillaria attramentaria

To address the impacts of past climate changes, particularly since the last glacial period, on the history of the distribution and demography of marine species, we investigated the evolutionary and demographic responses of the intertidal batillariid gastropod, Batillaria attramentaria, to these changes, using the snail as a model species in the northwest Pacific. We applied phylogeographic and divergence population genetic approaches to mitochondrial COI sequences from B. attramentaria. To cover much of its distributional range, 197 individuals collected throughout Korea and 507 publically available sequences (mostly from Japan) were used. Finally, a Bayesian skyline plot (BSP) method was applied to reconstruct the demographic history of this species. We found four differentiated geographic groups around Korea, confirming the presence of two distinct, geographically subdivided haplogroups on the Japanese coastlines along the bifurcated routes of the warm Tsushima and Kuroshio Currents. These two haplogroups were estimated to have begun to split approximately 400,000 years ago. Population divergence analysis supported the hypothesis that the Yellow Sea was populated by a northward range expansion of a small fraction of founders that split from a southern ancestral population since the last glacial maximum (LGM: 26,000–19,000 years ago), when the southern area became re‐submerged. BSP analyses on six geographically and genetically defined groups in Korea and Japan consistently demonstrated that each group has exponentially increased approximately since the LGM. This study resolved the phylogeography of B. attramentaria as a series of events connected over space and time; while paleoceanographic conditions determining the connectivity of neighboring seas in East Asia are responsible for the vicariance of this species, the postglacial sea‐level rise and warming temperatures have played a crucial role in rapid range shifts and broad demographic expansions of its populations.     

The parapatric distribution and contact zone of two forms showing different male-to-male aggressiveness in a social spider mite, Stigmaeopsis miscanthi (Acari: Tetranychidae)

Two forms showing different male-to-male aggressiveness, different male morphologies and different diapause attributes are known in Stigmaeopsis miscanthi (Saito), a social spider mite infesting Chinese silver grass (Miscanthus sinensis Anderss). Reproductive isolation exists between the forms, although it is not always complete, and the details of their distributional patterns are unknown, but expected to be parapatric. We searched for the contact zone at Mt. Unzen (Nagasaki Pref., Japan) where both forms are known to occur at different altitudes. We found the two forms together in several M. sinensis stands, suggesting there is frequent contact between the forms in their boundary area. We discuss the mechanism(s) that maintain the parapatry related to their frequent contact and the pattern of reproductive isolation between them.     

Population growth of Varroa destructor (Acari: Varroidae) in commercial honey bee colonies treated with beta plant acids

Varroa (Varroa destuctor Anderson and Trueman) populations in honey bee (Apis mellifera L.) colonies might be kept at low levels by well-timed miticide applications. HopGuard^® (HG) that contains beta plant acids as the active ingredient was used to reduce mite populations. Schedules for applications of the miticide that could maintain low mite levels were tested in hives started from either package bees or splits of larger colonies. The schedules were developed based on defined parameters for efficacy of the miticide and predictions of varroa population growth generated from a mathematical model of honey bee colony–varroa population dynamics. Colonies started from package bees and treated with HG in the package only or with subsequent HG treatments in the summer had 1.2–2.1 mites per 100 bees in August. Untreated controls averaged significantly more mites than treated colonies (3.3 mites per 100 bees). By October, mite populations ranged from 6.3 to 15.0 mites per 100 bees with the lowest mite numbers in colonies treated with HG in August. HG applications in colonies started from splits in April reduced mite populations to 0.12 mites per 100 bees. In September, the treated colonies had significantly fewer mites than the untreated controls. Subsequent HG applications in September that lasted for 3 weeks reduced mite populations to levels in November that were significantly lower than in colonies that were untreated or had an HG treatment that lasted for 1 week. The model accurately predicted colony population growth and varroa levels until the fall when varroa populations measured in colonies established from package bees or splits were much greater than predicted. Possible explanations for the differences between actual and predicted mite populations are discussed.     

Effects of physical and social experiences and octopamine receptor agonist on fighting behavior of male crickets Velarifictorus aspersus (Orthoptera: Gryllidae)

Fighting commonly occurs among animals and is very important for resolving conflicts between conspecific individuals over limited resources. The plasticity of fighting strategies and neurobiological mechanisms underlying fighting behavior of insects are not fully understood. In the present study, we examined whether physical and social experiences affected the aggressiveness of males of the cricket Velarifictorus aspersus Walker, and whether an octopamine (OA) receptor agonist could affected the aggressiveness of males exposed to different experiences. We found that flight and winning a fight significantly enhanced male aggressiveness, while losing a fight significantly suppressed male aggressiveness, consistent with the findings of existing studies on other cricket species. We also found that female presence had a stronger enhancing effect on male aggressiveness than flight or winning a fight. These findings demonstrated that physical and social experiences can affect the fighting behavior of male V. aspersus. Topical application of a 0.15?M solution of an OA receptor agonist (chlordimeform, CDM) significantly increased male aggression level, suggesting that OA may play an important role as a neuromodulator in controlling fighting behavior of males of this species. Despite displaying a significantly higher aggression level (level 5 or 6), CDM-treated losers did not escalate to physical combat, while fights between courting males usually resulted in physical escalation. It is likely that fighting behavior is only partly regulated by OA, and additional regulatory pathways may be involved in achieving physical combat.     

Interglacial genetic diversification of Moussonia deppeana (Gesneriaceae), a hummingbird‐pollinated,cloud forest shrub in northern Mesoamerica

Recent empirical work on cloud forest‐adapted species supports the role of both old divergences across major geographical areas and more recent divergences attributed to Pleistocene climate changes. The shrub Moussonia deppeana is distributed in northern Mesoamerica, with geographically disjunct populations. Based on sampling throughout the species range and employing plastid and nuclear markers, we (i) test whether the fragmented distribution is correlated with main evolutionary lineages, (ii) reconstruct its phylogeographical history to infer the history of cloud forest in northern Mesoamerica and (iii) evaluate a set of refugia/vicariance scenarios for the region and demographic patterns of the populations whose ranges expanded and tracked cloud forest conditions during the Last Glacial Maximum. We found a deep evolutionary split in M. deppeana about 6–3 Ma, which could be consistent with a Pliocene divergence. Comparison of variation in plastid and nuclear markers revealed several lineages mostly congruent with their isolated geographical distribution and restricted gene flow among groups. Results of species distribution modelling and coalescent simulations fit a model of multiple refugia diverging during interglacial cycles. The demographic history of M. deppeana is not consistent with an expanding–contracting cloud forest archipelago model during the Last Glacial Maximum. Instead, our data suggest that populations persisted across the geographical range throughout the glacial cycles, and experienced isolation and divergence during interglacial periods.     

Combining phylogeography and landscape genetics of Xenopipo atronitens (Aves: Pipridae), a white sand campina specialist,to understand Pleistocene landscape evolution in Amazonia

Open vegetation (campinas and campinaranas) associated with white sand patches occurs in the form of islands in a forested matrix throughout the Amazon basin. Bird species restricted to these habitats have patchy distributions, although connectivity may have been influenced by past glacial cycles as a result of the substitution of forest by savanna. Because these landscape changes are a matter of debate in the history of Amazonia, we studied the diversification of Xenopipo atronitens, a white sand specialist, aiming to infer the effects of past climate changes. The split of Xenopipo atronitens from its sister species, Xenopipo uniformis, may be related to Tepuis erosion and retreat of escarpments during the Miocene, or to a dispersal event. Compared with birds from terra firme forest, X. atronitens has low genetic structure. Low levels of unidirectional gene flow were found from the Guyana Shield to adjacent areas. Demographic expansion starting approximately 25 kyr BP was detected for some populations and is probably related to the Last Glacial Maximum and subsequent climate improvement. Landscape genetic analyses indicate that the forested (terra firme) matrix acts as a barrier for the dispersal of X. atronitens. The results of the present study indicate that glacial cycles have deeply influenced Amazonian biogeographical history, demonstrating a complex interaction between forest and nonforest habitats during the Pleistocene. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 110 , 60–76.     

The population demography of Betula maximowicziana,a cool‐temperate tree species in Japan,in relation to the last glacial period: its admixture‐like genetic structure is the result of simple population splitting not admixing

Conservation of the local genetic variation and evolutionary integrity of economically and ecologically important trees is a key aspect of studies involving forest genetics, and a population demographic history of the target species provides valuable information for this purpose. Here, the genetic structure of 48 populations of Betula maximowicziana was assessed using 12 expressed sequence tag–simple sequence repeat (EST‐SSR) markers. Genetic diversity was lower in northern populations than southern ones and structure analysis revealed three groups: northern and southern clusters and an admixed group. Eleven more genomic‐SSR loci were added and the demographic history of these three groups was inferred by approximate Bayesian computation (ABC). The ABC revealed that a simple split scenario was much more likely than isolation with admixture, suggesting that the admixture‐like structure detected in this species was due to ancestral polymorphisms. The ABC analysis suggested that the population growth and divergence of the three groups occurred 96 800 (95% CI, 20 500–599 000) and 28 300 (95% CI, 8700–98 400) years ago, respectively. We need to be aware of several sources of uncertainty in the inference such as assumptions about the generation time, overlapping of generations, confidence intervals of the estimated parameters and the assumed model in the ABC. However, the results of the ABC together with the model‐based maps of reconstructed past species distribution and palaeoecological data suggested that the modern genetic structure of B. maximowicziana originated prior to the last glacial maximum (LGM) and that some populations survived in the northern range even during the LGM.     

Historical biogeography and post-glacial recolonization of South American temperate rain forest by the relictual marsupial Dromiciops gliroides

Aim Long‐term climatic variation has generated historical expansions and contractions of species ranges, with accompanying fragmentation and population bottlenecks, which are evidenced by spatial variation in genetic structure of populations. We examine here hypotheses concerning dispersal and vicariance in response to historical geoclimatic change and potential isolation produced by mountains and water barriers. Location The temperate rain forest of southern South America, which is distributed from coastal Chile, including the large continental island of Chiloé, across the Andes into Argentina. Methods We investigated our hypotheses in the phylogenetically and biogeographically relictual marsupial Dromiciops gliroides. We examined 56 specimens, which resulted from field samples and museum study skins from 21 localities. We evaluated the influence of two major barriers, the Andean cordillera and the waterway between the mainland and the large island of Chiloé, by performing Bayesian and maximum‐likelihood phylogenetic analyses on sequences of 877 base pairs of mitochondrial DNA. We further tested the contribution of the proposed geographical barriers using analysis of molecular variance (amova ). We also evaluated the responses of populations to historical north–south shifts of habitat associated with glacial history and sea‐level change. Results Our analyses revealed a phylogeny with three clades, two of which are widespread and contain nearly all the haplotypes: a northern clade (36–39° S) and a southern clade (40–43° S). These two clades contain forms from both sides of the Andes. Within the southern clade, island and mainland forms were not significantly differentiated. Tests of recent demographic change revealed that southern populations have experienced recent expansion, whereas northern populations exhibit long‐term stability. The direction of recent gene flow and range expansion is predominantly from Chile to Argentina, with a modest reciprocal exchange across the Andes. Recent gene flow from the island of Chiloé to the mainland is also supported. Main conclusions The genetic structure of contemporary D. gliroides populations suggests recent gene flow across the Andes and between the mainland and the island of Chiloé. Differences in demographic history that we detected between northern and southern populations have resulted from historical southward shifts of habitat associated with glacial recession in South America. Our results add to a growing literature that demonstrates the value of genetic data to illuminate how environmental history shapes species range and population structure.     

Contrasting patterns of nuclear microsatellite genetic structure of Fraxinus mandshurica var. japonica between northern and southern populations in Japan

Aim The aim of this study is to detect extant patterns of population genetic structure of Fraxinus mandshurica var. japonica in Japan, and to provide insights into the post‐glacial history of this species during the Holocene. Location Hokkaido and Honshu islands, Japan (including the Oshima and Shimokita peninsulas). Methods We examined nine polymorphic nuclear microsatellite loci to assess genetic variation within and among 15 populations across almost the entire range of the species in Japan. Extant patterns of geographical structure were analysed using Bayesian clustering, Monmonier’s algorithm, analysis of molecular variance, Mantel tests and principal coordinates analysis. Recent bottlenecks within populations and regional genetic variation were also assessed. Results Northern populations (Hokkaido Island and the Shimokita Peninsula) formed a single homogeneous deme, maintaining the highest level of allelic diversity on the Oshima Peninsula. By contrast, southern populations (Honshu Island) demonstrated strong substructure on both coasts. Specifically, populations on the Pacific side of Honshu exhibited significant bottlenecks and erosion of allelic diversity but preserved distinct subclusters diverging from widespread subclusters on the Japan Sea side of this island. Main conclusions Genetic evidence and life history traits suggest that F. mandshurica occupied cryptic northern refugia on the Oshima Peninsula during the Last Glacial Maximum, which is reflected in the species’ extant northern distribution. Strong geographical structure in southern populations, in agreement with fossil pollen records, suggests geographical isolation by mountain ranges running north–south along Honshu. Given that this tree species is cold‐adapted and found in riparian habitats, populations on the Pacific side of Honshu probably contracted into higher‐elevation swamps during warm post‐glacial periods, leading to a reduction of effective population sizes and rare allelic richness.     

Adult-young interactions in island and mainland populations of the deermouse Peromyscus maniculatus

Summary The demographic and ecological characteristics of island populations of small mammals have received increasing attention in recent years, but few studies have compared the behavioral characteristics of island populations with those of mainland populations. Behavior is considered an important variable because it is believed by many to be a crucial factor affecting the population dynamics and demography of natural populations. In particular, among many species of rodents, the social behavior of adults towards juveniles is cited as an important factor influencing dispersal patterns and population regulation. The present study compares social interactions between adults and juveniles of island and mainland populations of the deermouse Peromyscus maniculatus, and attempts to relate differences in behavior to the demographic differences between the two populations. Adult mice were trapped on the mainland of British Columbia and on one of the Gulf Islands off the British Columbia coast, and allowed to breed in the laboratory. Male and female juveniles from both populations were then tested with their own parents and with unrelated male and female adults. The results demonstrate that island adults show almost no aggression towards either own or unrelated young. Mainland adults likewise show little aggression towards their own young, but a proportion of the population, consisting of both male and female adults, shows severe aggression towards unrelated juveniles of both sexes. These results suggest four major conclusions: 1) behavior may be the mechanism responsible for the demographic differences reported for these island and mainland populations; 2) female aggression may be a more important factor in deermouse population dynamics than has been previously recognized; 3) since parents show little aggression towards their own young, adult aggression may be a significant factor in juvenile mortality and emigration only after juveniles have initiated dispersal away from their natal sites; and 4) adult aggression controls the number of both male and female juveniles which are recruited into the population.     

Female Coalitions Against Male Aggression in Wild Chimpanzees of the Budongo Forest

In the wild, female chimpanzees (Pan troglodytes) are subject to male aggression that at times can be prolonged or particularly violent. There are no reports of cooperative retaliation to such aggression, a strategy observed in the congeneric Pan paniscus, from the wild despite >4 decades of detailed behavioral study across a number of populations and its occurrence among captive female chimpanzees. If the reports from captivity represent an inherent capacity, then the absence of similar reports from wild populations suggests that females may be able to form coalitions only under appropriate ecological and demographic conditions. During a study of male and female aggressive interactions among chimpanzees of the Budongo Forest, Uganda, wild adult female chimpanzees sometimes formed coalitions with one another to retaliate against male aggression. This may be possible because these females tend to be more gregarious than in other populations of East African chimpanzees, as other studies of the same population have suggested; the extent and variation of female chimpanzee social strategies may, therefore, need reconsideration. Further, my observations strengthen the argument that at least some of the differences between chimpanzees and bonobos may be more of degree than of kind.     

Phylogeography of Liquidambar styraciflua (Altingiaceae) in Mesoamerica: survivors of a Neogene widespread temperate forest (or cloud forest) in North America?

We investigate the genetic variation between populations of the American sweetgum (Liquidambar styraciflua), a tree species with a disjunct distribution between northeastern Texas and Mexico, by analyzing sequences of two chloroplast DNA plastid regions in Mesoamerica. Our results revealed phylogeographical structure, with private haplotypes distributed in unique environmental space at either side of the Trans‐Mexican Volcanic Belt, and a split in the absence of gene flow dating back ca. 4.2–1.4 million years ago (MYA). Species distribution modeling results fit a model of refugia along the Gulf and Atlantic coasts but the present ranges of US and Mesoamerican populations persisted disjunct during glacial/interglacial cycles. Divergence between the US and Mesoamerican (ca. 8.4–2.8 MYA) populations of L. styraciflua and asymmetrical gene flow patterns support the hypothesis of a long‐distance dispersal during the Pliocene, with fragmentation since the most recent glacial advance (120,000 years BP) according to coalescent simulations and high effective migration rates from Mesoamerica to the USA and close to zero in the opposite direction. Our findings implicate the Trans‐Mexican Volcanic Belt as a porous barrier driving genetic divergence of L. styraciflua, corresponding with environmental niche differences, during the Pliocene to Quaternary volcanic arc episode 3.6 MYA, and a Mesoamerican origin of populations in the USA.     

Intercontinental union of Argentine ants: behavioral relationships among introduced populations in Europe, North America, and Asia

Many invasive ants, including the Argentine ant Linepithema humile, form expansive supercolonies, within which intraspecific aggression is absent. The behavioral relationships among introduced Argentine ant populations at within-country or within-continent scales have been studied previously, but the behavioral relationships among intercontinental populations have not been examined. The present study investigated the levels of aggression among intercontinental Argentine ant populations by transporting live ants from Europe and California to Japan and conducting aggression tests against Japanese populations. Workers from the dominant supercolonies of Europe and California did not show aggressive behavior toward workers from the dominant supercolony of Japan, whereas they fought vigorously against workers from minor supercolonies. The three massive supercolonies, together with Argentine ants from Macaronesia, may be the largest non-aggressive unit formed by a social insect species in which intraspecific aggression exists. Absence or low levels of aggression at transcontinental scale, which may have derived from low genetic variation, may help introduced Argentine ants maintain expansive supercolonies. The lack of aggression implies possible frequent exchanges of individuals among the intercontinental populations mediated by human activities.