Diversity despite dispersal: colonization history and phylogeography of Hawaiian crab spiders inferred from multilocus genetic data

The Hawaiian archipelago is often cited as the premier setting to study biological diversification, yet the evolution and phylogeography of much of its biota remain poorly understood. We investigated crab spiders (Thomisidae, Mecaphesa ) that demonstrate contradictory tendencies: (i) dramatic ecological diversity within the Hawaiian Islands, and (ii) accompanying widespread distribution of many species across the archipelago. We used mitochondrial and nuclear genetic data sampled across six islands to generate phylogenetic hypotheses for Mecaphesa species and populations, and included penalized likelihood molecular clock analyses to estimate arrival times on the different islands. We found that 17 of 18 Hawaiian Mecaphesa species were monophyletic and most closely related to thomisids from the Marquesas and Society Islands. Our results indicate that the Hawaiian species evolved from either one or two colonization events to the archipelago. Estimated divergence dates suggested that thomisids may have colonized the Hawaiian Islands as early as ~10 million years ago, but biogeographic analyses implied that the initial diversification of this group was restricted to the younger island of Oahu, followed by back-colonizations to older islands. Within the Hawaiian radiation, our data revealed several well-supported genetically distinct terminal clades corresponding to species previously delimited by morphological taxonomy. Many of these species are codistributed across multiple Hawaiian Islands and some exhibit genetic structure consistent with stepwise colonization of islands following their formation. These results indicate that dispersal has been sufficiently limited to allow extensive ecological diversification, yet frequent enough that interisland migration is more common than speciation.     

Multiplication of the agent of X-disease in a non-vector leafhopper Macrostelesfascifrons

The relative titre of the causal agent of X-disease of stone fruits in the non-vector leafhopper Macrosteles fascifrons was tested by injecting dilutions of M. fascifrons extracts into non-infective Colladonus montanus leafhopper vectors. The recipient C. montanus were fed on celery test plants which were then observed for X-disease symptoms. M. fascifrons were assayed at various intervals for up to 37 days after they were fed on X-diseased celery or injected with infectious extracts of the X-agent. Infectivity was detected in M. fascifrons only after 25 or 37 days in separate trials. Whole body extracts but not extracts from detached heads of M. fascifrons that had fed on X-diseased celery were infectious, whereas extracts prepared from the heads of M. fascifrons previously injected with X-agent extracts were infectious. This infectivity was retained for up to four serial passages in M. fascifrons. Electron microscopy of M. fascifrons that had been injected with extracts of the X-disease agent revealed mycoplasma-like organisms (MLO) only intercellularly and appressed to various organs in the haemocoele. No MLO were observed in uninjected M. fascifrons or those injected with extracts from non-infectious C. montanus. These results suggest that, despite multiplication of the X-agent in vivo. barriers in the gut and salivary glands prevent its transmission to plants by M. fascifrons.     

Regulation and acclimation of leaf gas exchange in a piñon–juniper woodland exposed to three different precipitation regimes

Leaf gas‐exchange regulation plays a central role in the ability of trees to survive drought, but forecasting the future response of gas exchange to prolonged drought is hampered by our lack of knowledge regarding potential acclimation. To investigate whether leaf gas‐exchange rates and sensitivity to drought acclimate to precipitation regimes, we measured the seasonal variations of leaf gas exchange in a mature piñon–juniper Pinus edulis–Juniperus monosperma woodland after 3 years of precipitation manipulation. We compared trees receiving ambient precipitation with those in an irrigated treatment (+30% of ambient precipitation) and a partial rainfall exclusion (?45%). Treatments significantly affected leaf water potential, stomatal conductance and photosynthesis for both isohydric piñon and anisohydric juniper. Leaf gas exchange acclimated to the precipitation regimes in both species. Maximum gas‐exchange rates under well‐watered conditions, leaf‐specific hydraulic conductance and leaf water potential at zero photosynthetic assimilation all decreased with decreasing precipitation. Despite their distinct drought resistance and stomatal regulation strategies, both species experienced hydraulic limitation on leaf gas exchange when precipitation decreased, leading to an intraspecific trade‐off between maximum photosynthetic assimilation and resistance of photosynthesis to drought. This response will be most detrimental to the carbon balance of piñon under predicted increases in aridity in the southwestern USA.     

CONSUMER PERCEPTION OF WHEY AND SOY PROTEIN IN MEAL REPLACEMENT PRODUCTS

ABSTRACT

Meal replacement products including protein bars, shakes and powdered drinks have increased in demand and sales. The objective of this study was to assess the consumer perception of protein content and type and product claims for meal replacement beverages and bars. The impact of exercise frequency on product perception was also investigated. Focus groups were conducted with exercisers and nonexercisers. An adaptive conjoint analysis survey was subsequently developed and conducted (n = 138 consumers, ages 18–35 years). Relative importance of product attributes was determined through a realistic trade‐off scenario. Utility scores were extracted and rescaled by the zero‐centered differences method, and two‐way analysis of variance was conducted to identify the differences between exercise frequency and product attributes. Both groups preferred bars to beverages, and no clear preferences were observed for protein type, which was consistent with focus group results of low knowledge/understanding of specific proteins. All respondents valued the products with low‐fat/fat‐free, calcium, all‐natural, protein, vitamin/mineral, heart health and muscle‐building claims. Exercisers viewed muscle‐building claims as more important than nonexercisers. Nonexercisers viewed heart health, calcium and vitamin/mineral claims as more important than exercisers. Three distinct consumer clusters were identified, and both exercise groups were found in all three clusters, although exercise frequency influenced membership in two of the three clusters (P < 0.05). These findings can be used to develop and market meal replacement products to specific consumer groups while leveraging their specific and unique needs.

PRACTICAL APPLICATIONS

Conjoint analysis provides a useful model of how consumers think during the purchase process and an understanding of the motivation for purchase through the testing of possible claims or product attributes. By applying this method to the purchase process of meal replacement bars and beverages, those in the field of development of these products can benefit from this information by being able to understand the motivation for purchase by the targeted consumer.     

Life history of a dipteran predator (Scathophagidae: Acanthocnema) of insect egg masses in a northern California stream

1. Little is known about the predators of insect eggs in fresh waters. This study describes aspects of the life history of a scathophagid fly (Acanthocnema sp.), whose larvae are predators of aquatic insect eggs. 2. Because the Acanthocnema predator oviposits its eggs on the surface of aquatic insect egg masses, all insect egg masses were collected regularly within a 200‐m reach of Redwood Creek (California, U.S.A.) between September 2003 and June 2007. Acanthocnema predators were found predominantly within egg masses of the caddifly Neophylax rickeri (Trichoptera: Uenoidae). 3. There was a mean of 0.25 Acanthocnema individuals per N. rickeri egg mass (n = 2367 egg masses). In general, N. rickeri egg masses were more commonly found clustered in aggregations (93.7%) than singly (6.3%), and Acanthonema were found more often within the aggregations of N. rickeri (98.7%) compared to singly laid egg masses (1.3%). 4. The duration of the Acanthocnema predator life stages was: egg 2.9 ± 0.8 (mean ± SD) days, larva 15.6 ± 10.2 days, pupa 80.3 ± 24.9 days and adult 7.2 ± 4.8 days. The short duration of the Acanthocnema egg stage (1–7 days) compared to that of its prey N. rickeri (2–4 weeks) raises the probability that the undeveloped eggs of N. rickeri would be available to the young predators upon hatching. Egg consumption of N. rickeri eggs by Acanthocnema averaged 262.6 eggs per larval period. 5. Acanthocnema had a bivoltine life cycle in which the first generation fed exclusively on N. rickeri egg masses in the winter and the second generation fed on the egg masses of several species, including other Trichoptera (Brachycentridae) and Diptera (Ceratopogonidae, Chironomidae) in the spring. These findings suggest differing feeding strategies by the first and second generations of Acanthocnema in response to the seasonal availability of prey species. This type of autecological information is important for understanding mechanisms of community interactions.     

Century‐scale records of coral growth rates indicate that local stressors reduce coral thermal tolerance threshold

Coral bleaching, during which corals lose their symbiotic dinoflagellates, appears to be increasing in frequency and geographic extent, and is typically associated with abnormally high water temperatures and solar irradiance. A key question in coral reef ecology is whether local stressors reduce the coral thermal tolerance threshold, leading to increased bleaching incidence. Using tree‐ring techniques, we produced master chronologies of growth rates in the dominant reef builder, massive Montastraea faveolata corals, over the past 75–150 years from the Mesoamerican Reef. Our records indicate that the 1998 mass bleaching event was unprecedented in the past century, despite evidence that water temperatures and solar irradiance in the region were as high or higher mid‐century than in more recent decades. We tested the influence on coral extension rate from the interactive effects of human populations and thermal stress, calculated here with degree‐heating‐months (DHM). We find that when the effects of chronic local stressors, represented by human population, are taken into account, recent reductions in extension rate are better explained than when DHM is used as the sole predictor. Therefore, the occurrence of mass bleaching on the Mesoamerican reef in 1998 appears to stem from reduced thermal tolerance due to the synergistic impacts of chronic local stressors.