Distinguishing coevolution from covicariance in an obligate pollination mutualism: asynchronous divergence in Joshua tree and its pollinators

Obligate pollination mutualisms--in which both plants and their pollinators are reliant upon one another for reproduction--represent some of the most remarkable coevolutionary interactions in the natural world. The intimacy and specificity of these interactions have led to the prediction that the plants and their pollinators may be prone to cospeciation driven by coevolution. Several studies have identified patterns of phylogenetic congruence that are consistent with this prediction, but it is difficult to determine the evolutionary process that underlies these patterns. Phylogenetic congruence might also be produced by extrinsic factors, such as a shared biogeographic history. We examine the biogeographic history of a putative case of codivergence in the obligate pollination mutualism between Joshua trees (Yucca brevifolia) and two sister species of pollinating yucca moths (Tegeticula spp.) We employ molecular phylogenetic methods and coalescent-based approaches, in combination with relaxed-clock estimates of absolute rates of molecular evolution, to analyze multi-locus sequence data from more than 30 populations of Y. brevifolia and its pollinators. The results indicate that the moth species diverged significantly (p < 0.01) more recently than their corresponding host populations, suggesting that the apparent codivergence is not an artifact of a shared biogeographic history.     

Absence of population-level phenotype matching in an obligate pollination mutualism

Coevolution is thought to promote evolutionary change between demes that ultimately results in speciation. If this is the case, then we should expect to see similar patterns of trait matching and phenotypic divergence between populations and between species in model systems for coevolution. As measures of divergence are frequently only available at one scale (population level or taxon level), this contention is rarely tested directly. Here, we use the case of co-divergence between different varieties of Joshua tree Yucca brevifolia (Agavaceae) and their obligate pollinators, two yucca moths (Tegeticula spp. Prodoxidae), to test for trait matching between taxa and among populations. Using model selection, we show that there is trait matching between mutualists at the taxon level, but once we account for differences between taxa, there is no indication of trait matching in local populations. This result differs from similar studies in other coevolving systems. We hypothesize that this discrepancy arises because coevolution in obligate mutualisms favours divergence less strongly than coevolution in other systems, such as host–parasite interactions.     

Costs of two non-mutualistic species in a yucca/yucca moth mutualism

Mutualisms often involve significant costs for participants. Costs are inflicted by mutualists themselves, as well as by associated, non-mutualistic species. These costs are rarely quantified, however, particularly the ones extrinsic to the pairwise interaction. We compare costs inflicted by an obligate mutualist pollinator and two common exploiters of an Arizona yucca over a 2-year period. The magnitude of seed damage from seed and fruit-feeding beetle larvae (Carpophilus longus, Nitidulidae) was similar to damage from the seed-eating larvae of Yucca schottii's pollinator moth Tegeticula yuccasella (Prodoxidae), averaging about 15 seeds destroyed per fruit in each case. The two seed predators usually fed within the same fruits, although rarely side by side. In contrast, the presence of fruit-galling moth larvae (Prodoxusy-inversus, Prodoxidae) appeared to benefit the yucca: individual Tegeticula destroyed only half as many seeds in galled fruits as they did in ungalled fruits. We discuss three general implications of these results. Firstly, the costs of non-mutualists to the two mutualistic partners are not necessarily parallel. Secondly, measurable costs of non-mutualists do not necessarily translate into an impact on the success of the mutualism itself, because they may be incurred after mutualistic activities take place. Finally, the costs of mutualists to each other can differ substantially depending on the presence or absence of non-mutualistic species. Received:17 July 1996 / Accepted:10 June 1997     

Some pollinators are more equal than others: Factors influencing pollen loads and seed set capacity of two actively and passively pollinating fig wasps

The nursery pollination system of fig trees (Ficus) results in the plants providing resources for pollinator fig wasp larvae as part of their male reproductive investment, with selection determining relative investment into pollinating wasps and the pollen they carry. The small size of Ficus pollen suggests that the quantities of pollen transported by individual wasps often limits male reproductive success. We assessed variation in fig wasp pollen loads and its influence on seed production in actively pollinated (Ficus montana) and passively pollinated (Ficus carica) dioecious fig trees.The ratios of number of male flowers on number of female flowers in a glasshouse-maintained F. montana population were highly variable. When fig wasps were introduced into receptive female figs, the resulting seed numbers were strongly linked to the numbers of pollinators that had been seeking access to pollen, relative to the number of anthers in their natal figs. In F. carica estimates of the amounts of pollen produced per fig and the quantities of pollen carried by emerging fig wasps suggest that less than 10% of the pollen is transported. Pollinators of F. carica that emerged earlier from figs carried more pollen, and also generated more seeds when introduced into receptive female figs.We show here that all pollinators are not equally valuable and producing more pollinators is not necessarily a good option in terms of Ficus male fitness. Previous results on F. montana figs showed that only around half of the flowers where pollinators lay eggs produced adult offspring. The amount of pollen collected by young female fig wasps may be a major determinant of their reproductive success.     

Response of the European grapevine moth Lobesia botrana to somatosensory‐active volatiles emitted by the non‐host plant Perilla frutescens

The European grapevine moth Lobesia botrana Denis & Schiffermüller (Lepidoptera: Tortricidae) is a major pest on grapes worldwide. Attempts to develop control methods for this pest based on grape kairomones demonstrate limited success and studies indicate that a major limiting factor is overlap between synthetic kairomones and background odours in the vineyard. Behaviourally active compounds from non‐host plants may thus represent an effective alternative for monitoring and control methods. Extracts from food plants (i.e. from capsicum, garlic and peppermint, which elicit the so‐called somatosensory sensation) are traditionally used in agriculture for the control of pest insects. Among those plants, Perilla frutescens L. (Lamiales: Lamiaceae), native of Asia, contains compounds activating sensory ion channels in mammals, which are known to be involved in the perception of somatosensory compounds and are expressed in tortricid moth antennae. In the present study, in search of non‐host volatiles with potential application in pest control, essential oil metabolites isolated from P. frutescens are screened for biological activity on the olfactory system of L. botrana. The compounds (S)‐(?)‐perillaldehyde and isoegomaketone, which are released from different P. frutescens varieties, are identified by gas chromatography‐coupled electroantennographic detection. In a dual‐choice oviposition test, females show a preference for a combination of host odours and perillaldehyde, preferring this over a host‐plant odour bouquet alone. In Y‐tube olfactometer assays, virgin males show a higher level of activity in the presence of isoegomaketone, even if not significantly responsive to the compound.     

Body size in a pollinating fig wasp and implications for stability in a fig‐pollinator mutualism

The fig–fig pollinator association is a classic case of an obligate mutualism. Fig‐pollinating wasps often have to fly long distances from their natal syconia to a receptive syconium and then must enter the narrow ostiole of the syconium to reproduce. Large wasps are expected to have a greater chance of reaching a receptive syconium. In this study, we tested this hypothesis and then examined whether the ostiole selectively prevented larger pollinators from entering the syconial cavity. In Xishuangbanna, China, Ceratosolen solmsi marchali Mayr (Hymenoptera: Agaonidae) pollinates the dioecious syconia of Ficus hispida L. (Moraceae). The body size of newly emerged wasps and wasps arriving at receptive syconia were compared. Wasps arriving at receptive syconia were significantly larger than newly emerged wasps. We also compared the size of wasps trapped in the ostiole with those in the cavity. Wasps trapped in the ostiole were significantly larger than those in the syconial cavity. Thus, in the case of F. hispida, large wasps were more likely to reach receptive syconia, but the ostiole limited maximum fig wasp size. This indicates that the ostiole, as a selective filter to pollinators, stabilizes pollinator size. Hence, it helps to maintain stability in the fig–fig pollinator mutualism.     

Reproductive strategies of two forms of flightless males in a non‐pollinating fig wasp under partial local mate competition

1. The underlying basis of alternative male reproductive strategies is either genetic or environmental. Several non‐pollinating fig wasp lineages have dimorphic males, typically with winged males that disperse from natal figs to mate and flightless males that seek mating opportunities in natal figs. 2. Walkerella sp. from Ficus benjamina has dark and pale wingless males. Observations and experiments in Xishuangbanna, Southern China found that (i) the sex ratio of Walkerella sp. did not vary with foundress number or brood size. (ii) The frequency of dark males increased with brood size and foundress number and they were absent from figs with a single foundress. This produced a higher proportion of dark males at higher densities. (iii) Males of both morphs fought, but injuries to dark males were more frequent. (iv) Dark males were more likely to disperse away from their natal figs and (v) they were more resistant to dehydration. 3. Responses to selection are constrained by the genetic options available. Consequently, selection pressures acting on different lineages can produce similar outcomes that are achieved in different ways. Walkerella species lack winged males, but dark males display some of their features, dispersing from natal figs and displaying appropriate physiological and behavioural adaptations. However, dark males also displayed increased levels of damage from fighting – a feature unlikely to be shared with the winged males of other species.     

Presence of weed fungus in a non‐social beetle–fungus cultivation mutualism

1. Farming by non‐human organisms has arisen independently in several animal lineages, allowing them to survive on food sources that are otherwise difficult to access. However, agricultural gardens are prone to invasion by parasites that overgrow cultivars in the absence of host animals. The presence of garden parasites and associated host adaptations are well studied in advanced fungal agriculture practised by social insects (ants, termites, and ambrosia beetles), but the impact of garden parasites in more primitive forms of agriculture is poorly known. The aim of the present study was to report the presence of weed fungi in fungal gardens of the non‐social lizard beetle Doubledaya bucculenta Lewis (Coleoptera: Erotylidae: Languriinae), which cultivates the yeast Wickerhamomyces anomalus (E.C. Hansen) Kurtzman, Robnett & Bas.‐Powers in the internodes of recently dead bamboo culms. 2. The filamentous fungi Arthrinium spp., Fusarium spp., and an unidentified species were isolated from the inner wall and insect‐made wall debris of bamboo internodes inhabited by the beetle. 3. When cultured together with the yeast in the absence of host larvae, Arthrinium sp.1 outcompeted the yeast, suggesting that this filamentous fungus can invade yeast gardens but is normally suppressed under natural conditions. 4. Rearing experiments showed that beetle larvae grew faster when grown on yeast cultures than when fed only Arthrinium sp.1. 5. These results suggest that Arthrinium sp.1 acts as a weed in the fungal gardens of D. bucculenta, inhibiting both growth of the beetle larvae and proliferation of the beneficial yeast.     

Contrasting behavior between two populations of an ice‐obligate predator in East Antarctica

The Austral autumn–winter is a critical period for capital breeders such as Weddell seals that must optimize resource acquisition and storage to provision breeding in the subsequent spring. However, how Weddell seals find food in the winter months remains poorly documented. We equipped adult Weddell seals after their annual molt with satellite‐relayed data loggers at two sites in East Antarctica: Dumont D'Urville (n = 12, DDU) and Davis (n = 20). We used binomial generalized mixed‐effect models to investigate Weddell seals’ behavioral response (i.e., “hunting” vs. “transit”) to physical aspects of their environment (e.g., ice concentration). Weddell seal foraging was concentrated to within 5 km of a breathing hole, and they appear to move between holes as local food is depleted. There were regional differences in behavior so that seals at Davis traveled greater distances (three times more) and spent less time in hunting mode (half the time) than seals at DDU. Despite these differences, hunting dives at both locations were pelagic, concentrated in areas of high ice concentration, and over areas of complex bathymetry. There was also a seasonal change in diving behavior from transiting early in the season to more hunting during winter. Our observations suggest that Weddell seal foraging behavior is plastic and that they respond behaviorally to changes in their environment to maximize food acquisition and storage. Such plasticity is a hallmark of animals that live in very dynamic environments such as the high Antarctic where resources are unpredictable.     

Population dynamics and economic losses caused by Zeuzera pyrina,a cryptic wood‐borer moth,in an olive orchard in Egypt

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Antennal mechanosensors mediate sex pheromone‐induced upwind orientation in the potato tuberworm moth

Males of the potato tuberworm moth Phthorimaea operculella (Lepidoptera: Gelechiidae) locate conspecific females by a series of short and straight flights, or ‘hops’. On the floor of a wind tunnel, P. operculella can change their heading angles in response to wind direction shift, suggesting that they detect wind direction and orient upwind when on the ground. It is unlikely that they navigate in wind by vision‐induced optomotor anemotaxis as in many flying moths. To investigate the mechanism of wind direction detection in this species, their orientation behaviour in response to pheromone pulses is observed in a wind tunnel. Intact male moths orient upwind even in complete darkness. After the flagellum of one antenna is amputated, male moths still successfully orient upwind. However, they fail to head upwind when the basal segments of both of their antennae are immobilized with glue. The ability to surge upwind is restored by removing the glue from the antennae. Thus, the results of the present study indicate that males of P. operculella orient upwind in response to mechanoreceptive cues from mechanosensory organs on their antennae. In Lepidoptera, two distinct anemotactic mechanisms of different sensory modalities appear to coexist: optomotor anemotaxis when airborne and the aim‐then‐shoot anemotactic system mediated by antennal mechanoreception when on the ground.     

Lack of genetic isolation by distance,similar genetic structuring but different demographic histories in a fig‐pollinating wasp mutualism

Historical abiotic factors such as climatic oscillations and extreme climatic events as well as biotic factors have shaped the structuring of species' genetic diversity. In obligate species‐specific mutualisms, the biogeographic histories of the interacting species are tightly linked. This could be particularly true for nuclear genes in the Ficus‐pollinating wasp mutualistic association as the insects disperse pollen from their natal tree. In this study, we compare spatial genetic structure of plant and pollinator for the Ficus hirta–Valisia javana association throughout southeast China including Hainan Island, for both nuclear and cytoplasmic markers. We show that dispersal of the insect leads to plant and insect presenting similar signatures of lack of genetic isolation by distance for nuclear genes on the continent over a distance of 1000 km. But we also show that the demographic histories of plant and insect are strikingly different. This is in agreement with extreme climatic events leading to transient regional extinctions of the insects, associated with local survival of the plants. We also observe evidence of genetic differentiation for both wasps and fig‐tree between the continent and Hainan Island, although the Qiongzhou Strait is only on average 30 km wide, suggesting that geographic isolation by itself has not been sufficient to generate this differentiation. Hence, our results suggest that in highly dispersive mutualistic systems, isolation‐by‐dispersal limitation across a geographic barrier could be supplemented by isolation by adaptation, and maybe by coevolution, allowing further genetic divergence. In such systems, species may frequently be composed of a single population.     

Ecological effects of non‐native species in marine ecosystems relate to co‐occurring anthropogenic pressures

Predictors for the ecological effects of non‐native species are lacking, even though such knowledge is fundamental to manage non‐native species and mitigate their impacts. Current theories suggest that the ecological effects of non‐native species may be related to other concomitant anthropogenic stressors, but this has not been tested at a global scale. We combine an exhaustive meta‐analysis of the ecological effects of marine non‐native species with human footprint proxies to determine whether the ecological changes due to non‐native species are modulated by co‐occurring anthropogenic impacts. We found that non‐native species had greater negative effects on native biodiversity where human population was high and caused reductions in individual performance where cumulative human impacts were large. On this basis we identified several marine ecoregions where non‐native species may have the greatest ecological effects, including areas in the Mediterranean Sea and along the northwest coast of the United States. In conclusion, our global assessment suggests coexisting anthropogenic impacts can intensify the ecological effects of non‐native species.     

Specificity of Developmental Resistance in Gypsy Moth （Lymantria dispar） to two DNA-Insect Viruses

Gypsy moth (Lymantria dispar) larvae displayed marked developmental resistance within an instar to L. dispar M nucleopolyhedrovirus (LdMNPV) regardless of the route of infection (oral or intrahemocoelic) in a previous study, indicating that in gypsy moth, this resistance has a systemic component. In this study, gypsy moth larvae challenged with the Amsacta moorei entomopoxvirus (AMEV) showed developmental resistance within the fourth instar to oral, but not intrahemocoelic, inoculation. In general, gypsy moth is considered refractory to oral challenge with AMEV, but in this study, 43% mortality occurred in newly molted fourth instars fed a dose of 5×10⁶ large spheroids of AMEV; large spheroids were found to be more infectious than small spheroids when separated by a sucrose gradient. Developmental resistance within the fourth instar was reflected by a 2-fold reduction in mortality (18%–21%) with 5×10⁶ large spheroids in larvae orally challenged at 24, 48 or 72 h post-molt. Fourth instars were highly sensitive to intrahemocoelic challenge with AMEV; 1PFU produced approximately 80% mortality regardless of age within the instar. These results indicate that in gypsy moth, systemic developmental resistance may be specific to LdMNPV, reflecting a co-evolutionary relationship between the baculovirus and its host.     

Highly efficient pollination by bumblebees ensures seed production in Pedicularis lachnoglossa (Orobanchaceae), an early‐flowering Himalayan plant

Abstract Pedicularis (Orobranchaceae) is a common high altitude genus of the Himalayas that may be affected by pollination limitation. Using Pedicularis lachnoglossa from Yulong (Jade Dragon) Snow Mountain in Lijiang (Yunnan Province, southwest China), we investigated the effects of high altitude habitats on the process of pollination and seed production. Floral biology, pollinator foraging behavior, breeding system, and pollination efficiency were examined using observation and exclusionary techniques. Pedicularis lachnoglossa was found to be entomophilous and exclusively pollinated by Bombus friseanus and B. yunnanicola. Our results indicated that pollination limitation in P. lachnoglossa was not significant. Under open pollination, approximately 80% of flowers were successfully pollinated and developed to fruits, and about 38% of ovules developed to mature seeds. Bumblebee pollination is highly precise and efficient in P. lachnoglossa, because its flowering phenology and floral characters enhance the foraging of bumblebees on flowers. This study supports that animal pollination plays a crucial role in the outbreeding of the early flowering Pedicularis. The evolution of floral specification in Pedicularis has the advantages of adaptation to bumblebee pollination in adverse high altitude habitats.     

Determining the number of instars in potato tuber moth Phthorimaea operculella (Zeller) using density‐based DBSCAN clustering

The potato tuber moth (PTM), Phthorimaea operculella (Zeller), is an important pest of Solanaceae crops and especially devastating to potatoes. There is no significant difference in morphological characteristics of PTM from the first to third instar larvae; therefore, it is difficult to directly determine the number of instars of this pest based on morphology. In the present study, head capsule width and length and mandible width of 340 PTM individuals were measured. Density‐based spatial clustering of applications with noise (DBSCAN) clustering was used for instar grouping. The results of DBSCAN clustering were compared with those obtained using Gaussian mixture models and k‐means clustering; the results of the three clustering methods were verified using Brooks–Dyar rule, Crosby rule and linear regression model. The clusters obtained using the three methods were the same and comprised four PTM instars with three morphological characteristics. Moreover, the results of the three methods fit the Brooks–Dyar rule, Crosby rule, frequency analysis and logarithmic regression model well. Head capsule width was the best morphological characteristic for determining the number of instars of PTM, and this characteristic may be used for determining PTM instars in the field. These results show that the DBSCAN clustering method is a promising tool for the identification of insect instars.     

Patterns of seed longevity and dormancy in obligate seeding legumes of box‐ironbark forests,south‐eastern Australia

Current fuel loads and distribution suggest that fire events are infrequent and of a low intensity in the regenerated dry sclerophyll forests of the Victorian box‐ironbark ecosystem. However, many box‐ironbark species possess traits consistent with fire‐cued regeneration. It is unclear the degree to which human disturbance may have altered fire regimes in these forests. The infrequent and low‐intensity fire regime suggested by current fuel dynamics may pose a threat to the persistence of fire‐cued species. Obligate seeders such as those of the Fabaceae and Mimosaceae, common in box‐ironbark understoreys, may be particularly vulnerable if inter‐fire intervals exceed seed longevity. This study used seed burial trials to examine seed dormancy and longevity in five legume species to explore their capacity to regenerate under an infrequent, low‐intensity fire regime. All species displayed dormancy and longevity patterns consistent with other south‐east Australian legumes. Before burial, dormancy levels were high for all species (98–100%). After 3 years, storage under in situ and ex situ conditions, dormancy in Pultenaea prostrata remained at pre‐burial levels with virtually no seed becoming non‐dormant. Over time, some Acacia seed became non‐dormant under both in situ and ex situ storage, with the pattern varying among species. Longevity also varied between species. Variation in the dormancy and longevity patterns observed in these obligate seeder legumes suggests two strategies: (i) releasing a portion of soil‐stored seed from dormancy during the inter‐fire period to permit inter‐fire recruitment; and (ii) retaining most soil‐stored seed as dormant during the inter‐fire interval. Both strategies represent potential weaknesses under a long fire interval regime. The first relies on dormancy release translating to successful recruitment and requires ongoing inter‐fire input into the soil seed bank. The second relies on seed longevity exceeding the inter‐fire interval. Whether either is more suitable to coping with long‐term infrequent fire requires long‐term monitoring.     

Sex‐biased seed predation in gynodioecious Dianthus superbus var. longicalycinus (Capryophyllaceae) and differential influence of two seed predator species on the floral traits

Gynodioecy, the co‐occurrence of hermaphrodite and female individuals within a species, is maintained by differential reproductive success between sexes. Recently, researchers recognized that not only pollinators but also herbivores are important agents in the evolution and maintenance of gynodioecy, when herbivory is hermaphrodite biased. In this study, we investigated whether there is hermaphrodite‐biased herbivory in a gynodioecious plant, Dianthus superbus var. longicalycinus, and if so, what floral traits influenced hermaphrodite‐biased herbivory. We measured flower morphology (flower diameter, calyx tube length, corolla height and petal width) and phenology of flowers of female individuals, hermaphrodites and gynomonoecious individuals in a natural population. We also investigated seed predation and predator species. At the study site, Sibinia weevils (Curculionidae; Coleoptera) and Coleophora moths (Coleophoridae; Lepidoptera) were common pre‐dispersal seed predators in this species. The weevil appeared early in the flowering season, and weevil predation correlated with flower phenology. Because female individuals did not flower early in the season, weevil predation was less frequent in female individuals. Moth predation correlated with calyx length. The calyx length of flowers of female individuals was smaller than those of hermaphrodites, but a direct comparison of moth predation rates failed to find a significant difference among sex morphs. We found that the two seed predators had different effects on floral traits in D. superbus var. longicalycinus. We suggest that weevil predation contributes to the maintenance of gynodioecy because female individuals successfully escaped weevil predation by flowering late. It remains unclear why flower phenology is different among sex morphs.     

Ecological characteristics of a cave‐dwelling moth species,Triphosa dubitata (Lepidoptera: Geometridae), in Baram and Ssang caves in Gangwon Province,Korea

This study was performed to clarify the ecological characteristics of a cave‐dwelling moth species, Triphosa dubitata Linnaeus (Lepidoptera: Geometridae), at Baram cave and at Ssang cave within Pyeongchang‐gun of Gangwon province in south Korea. We investigated T. dubitata population for 3 days from March 2013 to October 2013 (except September) and in January 2014. We used a section investigation method in the caves every month to determine their ecological characteristic. A nocturnal investigation using a high intensity discharge lamp adjacent to the entrance of the cave was conducted in parallel with a diurnal investigation using butterfly traps to investigate the movement of T. dubitata. In order to investigate the range of habitat temperature of moths, we used a dual laser targeting infrared thermometer to measure the cave temperatures. We caught individuals of T. dubitata L.: 8,574 individuals in Baram cave and 828 individuals in Ssang cave. As 9,095 individuals (97 %) appeared at a temperature of ?3°C ~ 8°C, it was verified that the adults were living at specific temperatures. In addition, T. dubitata adults were not active outside the caves; they entered the cave as soon as they developed from pupa into adults. These results showed that T. dubitata depended on food plants outside of the cave during the egg–larva–pupa stages, and they used the cave as a habitat for long‐term survival when they develop into adults.