Evolution of fruit types and seed dispersal:A phylogenetic and ecological snapshot

Success of flowering plants is greatly dependent on effective seed dispersal. Specific fruit types aid different mechanisms of seed dispersal. However, little is known about what evolutionary forces have driven the diversification of fruit types and whether there were phylogenetic constraints on fruit evolution among angio-sperm lineages. To address these questions, we first surveyed the orders and families of angiosperms for fruit types and found no clear association between fruit types and major angiosperm lineages, suggesting there was little phylogenetic constraint on fruit evolution at this level. We then surveyed fruit types found in two contrasting habitats: an open habitat including the Indian desert and North American plains and prairies, and a closed forest habitat of Australian tropical forest. The majority of genera in the survey of tropical forests in Australia were fleshy fruit trees, whereas the majority of genera in the survey of prairies and plains in central North America were herbs with capsules and achenes. Both capsules and achenes are frequently dispersed by wind in the open, arid habitat, whereas fleshy fruits are generally dispersed by animals. Since desert and plains tend to provide continuous wind to aid dispersal and there are more abundant mammal and bird dispersers in the closed forest, this survey suggests that fruit evolution was driven at least in part by dispersal agents abundant in particular habitats.     

果实类型和种子传播的进化:系统发育和生态学简论

Success of flowering plants is greatly dependent on effective seed dispersal. Specific fruit types aid different mechanisms of seed dispersal. However, little is known about what evolutionary forces have driven the diversification of fruit types and whether there were phylogenetic constraints on fruit evolution among angiosperm lineages. To address these questions, we first surveyed the orders and families of angiosperms for fruit types and found no clear association between fruit types and major angiosperm lineages, suggesting there was little phylogenetic constraint on fruit evolution at this level. We then surveyed fruit types found in two contrasting habitats an open habitat including the Indian desert and North American plains and prairies, and a closed forest habitat of Australian tropical forest. The majority of genera in the survey of tropical forests in Australia were fleshy fruit trees, whereas the majority of genera in the survey of prairies and plains in central North America were herbs with capsules and achenes. Both capsules and achenes are frequently dispersed by wind in the open, arid habitat, whereas fleshy fruits are generally dispersed by animals. Since desert and plains tend to provide continuous wind to aid dispersal and there are more abundant mammal and bird dispersers in the closed forest, this survey suggests that fruit evolution was driven at least in part by dispersal agents abundant in particular habitats.     

携播螨与昆虫

文中指明了螨和昆虫之间的携播现象以及携播螨的特点 ,并讨论了螨和昆虫之间的携播现象与人类的关系。     

Phoresy in the field: natural occurrence of Trichogramma egg parasitoids on butterflies and moths

Phoretic insects utilize other animals to disperse to new environments. We recently discovered how egg parasitoids use an exciting phoretic strategy to reach egg-laying sites of their butterfly hosts. In the laboratory, female Trichogramma wasps detect and mount mated female cabbage white butterflies that emit an anti-aphrodisiac pheromone. Hardly any information exists about the natural occurrence of phoresy in wasps of this genus. Therefore, we monitored the presence of phoretic Trichogramma wasps on lepidopteran hosts in the field. Only female wasps were found at low prevalence on six lepidopteran species. Wasps were mostly found on female hosts and mainly on abundant solitary host species. This is the first report of phoretic Trichogramma wasps on butterflies in nature. We suggest that phoresy is only one of several strategies used by these polyphagous egg parasitoids. The evolution of phoresy is discussed in relation to the nutritional ecology of egg parasitoids.     

Importance of phoresy in the transmission of Acarina

Dispersal capacity plays a central role in the radiation of animals, facilitating the exploitation of habitats variously distributed in space or in time or both. Many living species are unable to leave a host, crawl around, and find a new host, so they must rely on external factors to be transmitted. Biotical factors may be important in passive transport and the process, by means of which an animal is passively transported by a selected carrier of different species, is known as "phoresy". Phoresy is a phenomenon in which one animal (the phoretic) seeks out and attaches to an animal of another species, with which it does not share any phase of the life cycle, for dispersal, during which time the phoretic animal becomes quiescent, stopping feeding and development. Activity starts again beginning with detachment, induced by stimuli originating from its carrier or the microhabitat. The adaptive traits of phoresy may be categorized as follow: host surface, quiescence, recognition of signals to abandon the carrier and, if needed, synchronization with the host life cycle. Phoresy is exploited by many Arthropods. In Acarina, there are basically four main types of phoresy. First, there is a type in which adult females are the only forms becoming phoretic and attachment is by means of chelicerae, palpal hooks and ambulacral claws, which grasp a seta or a fold of the integument of carrier-host. The second type is represented by mites, in which deutonymphs are phoretic; there is generally no cheliceral or sucker attachment in this group, mites instead hanging on by their ambulacral claws. The third type is similar to the second in that deutonymphs are phoretic; however, in this case, attachment to the host is by means of an anal pedicel formed by a substance, extruded through the anus, which hardens upon coming in contact with air and literally glues the mite to its host. In the fourth type there is a very highly modified deutonymph stage, called hypope, which only occurs at certain times, presumably when environmental conditions are no longer appropriate for the mite. Hypope is simplified morphologically, may have many sucker-like discs or claspers for efficient attachment, and is much more resistant to desiccation than are other stages of the life cycle.     

The distributions of parthenogenetic ascid mites (Acari: Parasitiformes) do not support the biotic uncertainty hypothesis

Fifteen out of 50 species of ascid mites (30%) that we collected from four synanthropic and seven natural habitats in North America and Australia existed as all-female populations. In contrast to the predictions of the biotic uncertainty hypothesis (i.e. that parthenogenetic species are rare, restricted in distribution and survive through dispersal ability), we found that parthenogentic ascid mites were present in ten out of 11 habitats sampled, but were not superior colonists. In a glasshouse experiment, pasteurized soil in pots was colonized first by bisexual species and only later by all-female species. Furthermore, a habitat requiring strong dispersal abilities (decaying fungal sporocarps) lacked parthenogenetic species and a review of literature and collections indicated that all-female ascid species rarely form the phoretic associations with insects necessary to exploit patchy and ephemeral resources. The assumptions that parthenogens are reproductively superior to but competitively inferior to sexual relatives were not supported by experiments comparing a bisexual and an all-female species of Lasioseius.     

PHORESY AS MIGRATION - SOME FUNCTIONAL ASPECTS OF PHORESY IN MITES

I. The dispersive role of mite phoresy, which has merely been presumed, is presented in the light of modern theories of migration with the aim of its characterization behaviourally, ecologically and physiologically. II. Data on phoresy accords well with modern, behavioural definitions of migration, as a phase of the depression of growth-promoting functions, during which the phoretic mite is transported while it shows a special readiness for being moved. III. Thus, modern definitions of migration encompass ‘passive’ movements which, none the less, involve active phases of seeking out of the host. IV. An examination of mite loads suggests that phoresy is most effective where the host gathers within the range of the mite; hence the association of phoresy with micro-habitats between which the mite requires to be carried. Monocultural plant-stands and ecological climaxes are not characterized by phoretic associations. V. The role of phoretic mites in colonization is clarified, in that phoretic migration is associated with sub-climactic communities. Thus, phoresy is invited where habitats are discrete and temporary, in which case it is manifest, as typical of migration, as a means of colonizing and exploiting irregularly changing habitats by r-selected, pre-reproductive individuals. VI. Waiting-stages, marked by the depression of growth-promoting functions, occur within the life-cycle of the phoretic mite. The ‘hypopus facies' characterize the typical phoretic stage, whose association with the host is an adaptation for survival in extreme environments. VII. Attachment pattern is a function of specificity towards the host. Structural and behavioural adaptations for attachment are developed and some sensory mechanisms have been shown, as have some physiological relationships with changes in the substrate; these changes also affect detachment. VIII. That phoresy is not caused by unfavourable conditions but is related to those that allow optimum dispersal is supported by sound evidence. IX. Physiologically, waiting stages have analogies with diapause which, together with migration, have been characterized by a temporary failure of the migrant to respond, by further growth and development, to the conditions that will eventually promote these processes. X. With phoresy are contrasted relations, between mite and insect, where the association is assured and more or less permanent. XI. The study of phoresy is very fragmented. However, a case has now been made for putting the dispersive role of phoresy beyond presumption, so that phoretic associations can clearly be fitted into modern treatments of migration.     

Correlation between the animal community structure and environmental factors in Jialiang and Boduo caves of Guizhou Province, China

1045 samples collected in Boduo cave belong to 3 phyla, 6 classes, 13 orders, 27 families and 45 species or groups. 469 samples collected in Jialiang cave were subordinated to 3 phyla, 6 classes, 9 orders, 24 families and 52 species or groups. According to the analysis of the community diversity, the communities that have the highest values of richness, diversity, maximum diversity, evenness, dominance and community similarity are D (8.3223), D (3.4677), D (3.8286), D (0.9057), C (0.0404) and D-E (0.6611), respectively. According to the analysis of Pearson correlation, the content of organic matter in soil is strongly positively related to species number, species richness, community diversity and maximum community diversity, and is significantly positively related to the evenness. The content of CO2 in air is opposite to the above result and is negatively related to species number, species richness, community diversity, maximum community diversity and evenness. The results indicate that the contents of organic matter and CO2 are the important factors influencing the community structure of cave animals.     

Correlation between the animal community structure and environmental factors in Jialiang and Boduo caves of Guizhou Province, China

1045 samples collected in Boduo cave belong to 3 phyla, 6 classes, 13 orders, 27 families and 45 species or groups. 469 samples collected in Jialiang cave were subordinated to 3 phyla, 6 classes, 9 orders, 24 families and 52 species or groups. According to the analysis of the community diversity, the communities that have the highest values of richness, diversity, maximum diversity, evenness, dominance and community similarity are D (8.3223), D (3.4677), D (3.8286), D (0.9057), C (0.0404) and D-E (0.6611), respectively. According to the analysis of Pearson correlation, the content of organic matter in soil is strongly positively related to species number, species richness, community diversity and maximum community diversity, and is significantly positively related to the evenness. The content of CO2 in air is opposite to the above result and is negatively related to species number, species richness, community diversity, maximum community diversity and evenness. The results indicate that the contents of organic matter and CO2 are the important factors influencing the community structure of cave animals.     

Review. When to leave the brood chamber? Routes of dispersal in mites associated with burying beetles

Most nests of brood-caring insects are colonized by a rich community of mite species. Since these nests are ephemeral and scattered in space, phoresy is the principal mode of dispersal in mites specializing on insect nests. Often the mites will arrive on the nest-founding insect, reproduce in the nest and their offspring will disperse on the insect's offspring. A literature review shows that mites reproducing in the underground brood chambers of burying beetles use alternative routes for dispersal. For example, the phoretic instars of Poecilochirus spp. (Mesostigmata: Parasitidae) disperse early by attaching to the parent beetles. Outside the brood chamber, the mites switch host at carcasses and pheromone-emitting male beetles, where juvenile and mature burying beetles of several species congregate. Because they preferably switch to beetles that are reproductively active and use all species of burying beetles within their ranges, they have a good chance of arriving in a new brood chamber. Other mite associates of burying beetles (Alliphis necrophilus and Uropodina) disperse from the brood chamber on the beetle offspring. We suggest that these mites forgo the possible time gain of dispersing early on the parent beetles because their mode of attachment precludes host switching. Their phoretic instars, once attached, have to stay on their host and so only dispersing on the beetle offspring guarantees that they are present on reproducing burying beetles of the next season. The mites associated with burying beetles providean example of multiple solutions to one life history problem – how to find a new brood chamber for reproduction. Mites that have mobile phoretic instars disperse on the parent beetles and try to arrive in the next brood chamber by host switching. They are independent of the generation cycle of a single host and several generations of mites per host generation are possible. Mites that are constrained by their mode of attachment disperse on the beetle offspring and wait until their host becomes mature and reproduces. By doing this they synchronize their generation time with the generation time of their host species. Exp Appl Acarol 22: 621–631 © 1998 Kluwer Academic Publishers     

Plant-mediated competition facilitates a phoretic association between a gall mite and a psyllid vector

Phoretic associations between mites and insects commonly occur in patchy and ephemeral habitats. As plants provide stable habitats for herbivores, herbivorous mites are rarely dependent on other animals for phoretic dispersal. However, a phoretic gall mite, Aceria pallida, which is found on plants, seasonally attaches to a herbivorous insect, Bactericera gobica, for overwintering survival. After detachment, the gall mite shares a habitat with its vector and is likely to compete with this vector for plant resources. However, excessive competition works against the sustainability of the seasonal phoretic association. How the gall mite, as an obligate phoretic mite, balances this relationship with its vector during the growing season to achieve phoresy is unknown. Here, the plant-mediated interspecific interaction between the gall mite and the psyllid after detachment was studied in the laboratory and field. The laboratory results showed that infestation by the gall mite had detrimental effects on the survival and development of psyllid nymphs. Meanwhile, the mite population and the gall size were also adversely affected. The results from the field showed that the mean densities of the mite galls and psyllids were lower in the mixed-species infestation treatment than in the single-species infestation treatment across the investigation period. However, the interspecific interaction between the gall mite and the psyllid decreased rather than accelerated leaf abscission caused by the psyllid, which promoted the persistence of the psyllid population and then indirectly contributed to phoretic association. Our results suggest that the plant-mediated competition between the phoretic gall mite and its vector after detachment facilitates the maintenance of the phoretic association.     

Review Reflections on the biology, morphology and ecology of the Macrochelidae

The Macrochelidae is a cosmopolitan family of predatory mesostigmatic mites, many of which occupy specialized and often unstable habitats. Most known species have adapted to life in dung deposits where prey is plentiful and the potential exists for rapid population growth. Phoresy on co-occurring flying insects plays a vital role in assuring niche continuity for macrochelids in these ephemeral substrates. A brief general review of some of the earlier highlights of macrochelid research is presented, followed by a discussion of the emergence of phoresy as a major survival strategy in the Macrochelidae associated with dung beetles. Special emphasis is placed on the behavioural and chemical mechanisms that mediate phoretic specificity of macrochelid species in the unique n-dimensional universes of their scarab hosts. Phylogenetic analysis of selected phoretic and non-phoretic macrochelid taxa has shown a strong correlation between phoretic state and evolutionary position, indicatin g that an increasing commitment to phoresy in the Macrochelidae is correlated with an advance from early derivative to terminal taxa. Laboratory and field observations have confirmed the importance of chemical, behavioural and ecological factors in maintaining the integrity of the relationship between phoretically specific macrochelids and their dung beetle hosts. © Rapid Science Ltd. 1998     

Phylogeography of cave pseudoscorpions in southern Australia

Aim  To investigate molecular phylogenetic divergence and historical biogeography of the cave-dwelling pseudoscorpion genus Protochelifer.
Location  Caves and nearby epigean habitats in southern Australia were sampled from western Victoria, Naracoorte Caves, Flinders Ranges, Kangaroo Island, Nullarbor Plain and south-west Western Australia.
Methods  Allozyme electrophoresis (57 individuals) and a 569-base-pair section of the mtDNA COI gene (22 individuals) were used to reconstruct phylogenetic relationships among four cave species and three epigean species from 13 locations.
Results  Phylogenetic reconstruction using the allozyme and mtDNA sequence data revealed a similar topology, showing recent speciation of several Protochelifer populations in caves from Naracoorte to the Nullarbor Plain. Naracoorte Caves contained a single species, Protochelifer naracoortensis , found in four separate caves, while all other cave species appear to be restricted to single caves.
Main conclusions  At a local scale, as indicated by the four Naracoorte caves, dispersal is thought to occur via micro- and mesocaverns, and possibly by phoresy using insect or bat vectors. With current data we are unable to determine if cavernicolous species of Protochelifer have arisen from a single cave colonization event followed by phoretic dispersal on bats to other caves, or multiple cave-invasion events from independent epigean ancestors. Genetic heterogeneity among Protochelifer populations from Nullarbor caves suggest that P. cavernarum , the only species presently recorded from this region, is likely to constitute a species complex requiring further study to fully resolve its relationships.     

贵州波多洞和甲良洞内部分环境因子与动物群落结构的相关性

在2002-2005年的2月和7月多次赴荔波波多洞和甲良洞对肉眼能见到的软体动物、节肢动物和脊索动物进行了观察和采集。在波多洞共获标本1045号,隶属3门6纲13目27科45种或类群,在甲良洞共获标本469号,隶属3门6纲9目24科52种或类群。根据上述两洞内各光带中动物种类和数量组成,可划分为6个动物群落。经群落多样性分析,物种丰富度、群落多样性、最大多样性、均匀度、优势度和相似性指数最高的分别是群落D（8.3223）、D（3.4677）、D（3.8286）、D（0.9057）、C（0.0404）和D-E（0.6611）。环境因子与群落多样性的相关分析结果显示：土壤中有机质的含量与物种数、物种丰富度、群落多样性和群落最大多样性指数都呈极显著正相关（相关系数分别为0.908、0.913、0.826和0.818）,与群落均匀度指数呈显著正相关（相关系数为0.674）;空气中CO2的含量与物种数、物种丰富度、群落多样性、群落最大多样性和均匀度指数都呈负相关（相关系数分别为-0.324、-0.552、-0.573、-0.345和-0.742）。这些结果暗示土壤有机质的含量和空气中CO2的含量是影响洞穴动物群落变化的重要因子。     

Potential role of parasitism in the evolution of mutualism in astigmatid mites: Hemisarcoptes cooremani as a model

Phoresy is a symbiotic interaction that results in dispersal, benefiting the relocated organism without negatively impacting the phoretic host. It has long been considered that phoresy among astigmatid mites is somehow an intermediate precursor to the evolution of parasitism within the group. In astigmatid mites, only the heteromorphic deutonymph (hypopode) participates in phoretic dispersal, and the plesiomorphic hypopode may be the key to understanding the dynamics of the evolution of that parasitism. Hypopodes of Hemisarcoptes cooremani (Acari: Acariformes) and their phoretic beetle host Chilocorus cacti (Coleoptera: Coccinellidae) have become the experimental focus for studies concerned with the potential forces that influence the transition of a free-living life style into various coevolved relationships. Previous radiolabeling studies applied to H. cooremani and C. cacti determined that hypopodes of H. cooremani acquired resources from adults of C. cacti while in transit, negating the paradigm that the heteromorphy was purely phoretic. To further probe this relationship, we tested whether materials could be passed from the mites to their hosts. We report here a study using a tritium radiolabel, which indicated that beetles also acquire resources from the hypopodes. These results have implications for understanding the complex relationship between H. cooremani and C. cacti. We propose that this relationship should now correctly be defined as mutualistic (not phoretic) and develop a general model for the potential role of parasitism in the evolution of mutualism among the Astigmata.     

Mycophagy in small mammals: A comparison of the occurrence and diversity of hypogeal fungi in the diet of the long-nosed potoroo Potorous tridactylus and the bush rat Rattus fuscipes from southwestern Victoria,Australia

Abstract Three broad dietary categories—fungus, plant and arthropod—were identified from faecal samples of two species of small terrestrial mammal in forest vegetation in southwestern Victoria. Fungal material formed the major component of the diet of the long-nosed potoroo Potorous tridactylus throughout the year and of the bush rat Rattus fuscipes during autumn and winter. Fungal material was most abundant for both species during autumn and winter and significantly less common in spring and summer. These results confirm previous studies which found P. tridactylus to be highly mycophagous throughout the year and R. fuscipes to be strongly mycophagous seasonally. Particular consideration was given to the composition of fungi in the diet. Fungal spores in faecal material were assigned to spore classes, which represent one or more fungal species that have similar spore morphology. Twenty-four fungal spore classes were recorded, but for both animal species most of the fungi consumed were from seven major spore classes. The proportions of major spore classes in the diet of both animals were generally similar, even though the composition of spore classes differed markedly across seasons. Minor differences between species in the fungi consumed may be related to differences in selectivity, foraging, or microhabitat use. If fungal resources are limiting, competition for such resources may be important in this and other small mammal communities. The amount and diversity of hypogeal fungi consumed by the two animal species makes them both important spore dispersal agents in forest ecosystems. The capacity of R. fuscipes and other seasonally mycophagous mammals in this role may be more important than previously recognized, especially in habitats where species of the Potoroidae are absent.     

Picky hitch‐hikers: vector choice leads to directed dispersal and fat‐tailed kernels in a passively dispersing mite

Dispersal is a central life‐history trait for most animals and plants: it allows to colonize new habitats, escape from competition or avoid inbreeding. Yet, not all species are mobile enough to perform sufficient dispersal. Such passive dispersers may use more mobile animals as dispersal vectors. If multiple potential vectors are available, an active choice can allow to optimize the dispersal process and to determine the distribution of dispersal distances, i.e. an optimal dispersal kernel. We explore dispersal and vector choice in the neotropical flower mite Spadiseius calyptrogynae using a dual approach which combines experiments with an individual‐based simulation model. Spadiseius calyptrogynae is found in lowland rainforests in Costa Rica. It inhabits inflorescences of the understorey palm Calyptrogyne ghiesbreghtiana and is phoretic on a number of flower visitors including bats, beetles and stingless bees. We hypothesised that the mites should optimise their dispersal kernel by actively choosing a specific mix of potential phoretic vectors. In a simple olfactometer setup we showed that the flower mites do indeed discriminate between potential vectors. Subsequently we used an individual‐based model to analyse the evolutionary forces responsible for the observed patterns of vector choice. The mites combine vectors exhibiting long‐distance dispersal with those allowing for more localized dispersal. This results in a fat‐tailed dispersal kernel that guarantees the occasional colonization of new host plant patches (long distance) while optimizing the exploitation of clumped resources (local dispersal). Additionally, kin competition results in a preference for small vectors that transport only few individuals at a time. At the same time, these vectors lead to directed dispersal towards suitable habitat, which increases the stability of this very specialized interaction. Our findings can be applied to other phoretic systems but also to vector‐based seed dispersal, for example.     

Species traits and environmental characteristics together regulate ant‐associated biodiversity

Host‐associated organisms (e.g., parasites, commensals, and mutualists) may rely on their hosts for only a portion of their life cycle. The life‐history traits and physiology of hosts are well‐known determinants of the biodiversity of their associated organisms. The environmental context may strongly influence this interaction, but the relative roles of host traits and the environment are poorly known for host‐associated communities. We studied the roles of host traits and environmental characteristics affecting ant‐associated mites in semi‐natural constructed grasslands in agricultural landscapes of the Midwest USA. Mites are frequently found in ant nests and also riding on ants in a commensal dispersal relationship known as phoresy. During nonphoretic stages of their development, ant‐associated mites rely on soil or nest resources, which may vary depending on host traits and the environmental context of the colony. We hypothesized that mite diversity is determined by availability of suitable host ant species, soil detrital resources and texture, and habitat disturbance. Results showed that that large‐bodied and widely distributed ant species within grasslands support the most diverse mite assemblages. Mite richness and abundance were predicted by overall ant richness and grassland area, but host traits and environmental predictors varied among ant hosts: mites associated with Aphaenogaster rudis depended on litter depth, while Myrmica americana associates were predicted by host frequency and grassland age. Multivariate ordinations of mite community composition constructed with host ant species as predictors demonstrated host specialization at both the ant species and genus levels, while ordinations with environmental variables showed that ant richness, soil texture, and grassland age also contributed to mite community structure. Our results demonstrate that large‐bodied, locally abundant, and cosmopolitan ant species are especially important regulators of phoretic mite diversity and that their role as hosts is also dependent on the context of the interaction, especially soil resources, texture, site age, and area.     

Joint evolution of dispersal and connectivity

Functional connectivity, the realized flow of individuals between the suitable sites of a heterogeneous landscape, is a prime determinant of the maintenance and evolution of populations in fragmented habitats. While a large body of literature examines the evolution of dispersal propensity, it is less known how evolution shapes functional connectivity via traits that influence the distribution of the dispersers. Here, we use a simple model to demonstrate that, in a heterogeneous environment with clustered and solitary sites (i.e., with variable structural connectivity), the evolutionarily stable population contains strains that are strongly differentiated in their pattern of connectivity (local vs. global dispersal), but not necessarily in the fraction of dispersed individuals. Also during evolutionary branching, selection is disruptive predominantly on the pattern of connectivity rather than on dispersal propensity itself. Our model predicts diversification along a hitherto neglected axis of dispersal strategies and highlights the role of the solitary sites—the more isolated and therefore seemingly less important patches of habitat—in maintaining global dispersal that keeps all sites connected.     

Failed predation or transportation? Causes and consequences of phoretic behavior in the pseudoscorpionDinocheirus arizonensis (Pseudoscorpionida: Chernetidae)

The pseudoscorpion Dinocheirus arizonensisinhabits rotting saguaro cactus in the Sonoran Desert and has also been found attached to the legs of the cactophilic neriid fly, Odontoloxozus longicornis.Laboratory experiments demonstrated a higher incidence of phoresy on eclosing versus postteneral adult flies, a female bias in phoresy, and an increased rate in female phoresy through time. The pseudoscorpion may also prey on the fly, but predation rate was unaffected by fly category, pseudoscorpion gender, or food deprivation. A study of pseudoscorpion colonization in the field indicated that females were the first to colonize and the first to abandon the transient habitat of a saguaro rot and, thus, corroborated patterns of phoretic behavior in the laboratory. Taken together, these results establish that phoresy is a behavior functioning specifically for dispersal. The hypothesis that pseudoscorpion transport by other arthropods is accidental, motivated by hunger, and occurs because pseudoscorpions are incapable of consuming their hosts is rejected.