Parasites exert conflicting selection pressures to affect reproductive asynchrony of their host plant in an obligate pollination mutualism

1. Plant reproductive phenology is generally viewed as an individual's strategy to maximize gamete exchange and propagule dispersal and is often considered largely dependent on patterns of floral initiation. Reproductive phenology, however, can be affected by proximate responses to pollinators, parasites and herbivores which could influence floral longevity or fruit development time. 2. We examined the influence of insect interactants on within-plant reproductive phenology in the fig-fig wasp nursery pollination mutualism in Ficus racemosa (Moraceae). Most figs support a wasp community comprised of a mutualistic pollinator, with several host-plant-specific non-pollinating herbivorous gallers and parasitoids. These wasps reproduce within enclosed inflorescences called syconia, which develop into fruit after pollination. While different wasp species oviposit into syconia at varying times during its ontogeny, all wasp progeny are constrained to exit syconia simultaneously just prior to fruit ripening. Developing larvae of early-ovipositing wasps may hasten syconium ontogeny through formation of earlier and larger nutrient sinks, whereas larvae of late-arriving parasites may lengthen syconium ontogeny to complete their development successfully. Seeds are also important nutrient sinks. The number of seeds and the type and number of developing wasps may therefore be expected to influence syconium development times, thereby affecting the reproductive synchrony of syconia on a plant. 3. Observations on naturally pollinated and parasitized syconia indicated that their seed and wasp content affected syconium development time. Experimental manipulations of syconia to produce only seeds or various combinations of wasps confirmed this finding. Early-ovipositing galler progeny reduced syconium development times, while gallers ovipositing concurrently with pollinators had no effect on syconium development. Late-ovipositing parasitoid progeny, the presence of only seeds within the syconium, or delayed pollination increased syconium development time. The differential development of syconia, which was influenced by mutualistic or parasitic progeny, accordingly contributed to within-tree reproductive asynchrony. 4. Synthesis. Individual reproductive units in fig trees called syconia, which also function as brood sites for pollinating and parasitic fig wasps, have plastic development durations dependent on pollination timing and species of wasps developing within them. Syconium development times are a likely compromise between conflicting demands from developing seeds and different wasp species.

Trophic level asynchrony in rates of phenological change for marine, freshwater and terrestrial environments

Recent changes in the seasonal timing (phenology) of familiar biological events have been one of the most conspicuous signs of climate change. However, the lack of a standardized approach to analysing change has hampered assessment of consistency in such changes among different taxa and trophic levels and across freshwater, terrestrial and marine environments. We present a standardized assessment of 25 532 rates of phenological change for 726 UK terrestrial, freshwater and marine taxa. The majority of spring and summer events have advanced, and more rapidly than previously documented. Such consistency is indicative of shared large scale drivers. Furthermore, average rates of change have accelerated in a way that is consistent with observed warming trends. Less coherent patterns in some groups of organisms point to the agency of more local scale processes and multiple drivers. For the first time we show a broad scale signal of differential phenological change among trophic levels; across environments advances in timing were slowest for secondary consumers, thus heightening the potential risk of temporal mismatch in key trophic interactions. If current patterns and rates of phenological change are indicative of future trends, future climate warming may exacerbate trophic mismatching, further disrupting the functioning, persistence and resilience of many ecosystems and having a major impact on ecosystem services.

Asynchrony between the Greenland ice core chronology and the radiocarbon calibration curve? Evidence from Irish bogs

A significant cold event, deduced from the Greenland ice cores, took place between 8200 and 8000 cal. BP. Modeling of the event suggests that higher northern latitudes would have also experienced considerable decreases in precipitation and that Ireland would have witnessed one of the greatest depressions. However, no well-dated proxy record exists from the British Isles to test the model results. Here we present independent evidence for a phase of major pine recruitment on Irish bogs at around 8150 cal. BP. Dendrochronological dating of subfossil trees from three sites reveal synchronicity in germination across the region, indicative of a regional forcing, and allows for high-precision radiocarbon based dating. The inner-rings of 40% of all samples from the north of Ireland dating to the period 8500-7500 cal. BP fall within a 25-yr window. The concurrent colonization of pine on peatland is interpreted as drier conditions in the region and provides the first substantive proxy data in support of a significant hydrological change in the north of Ireland accompanying the 8.2 ka event. The dating uncertainties associated with the Irish pine record and the Greenland Ice Core Chronology 2005 (GICC05) do not allow for any overlap between the two. Our results indicate that the discrepancy could be an artifact of dating inaccuracy, and support a similar claim by Lohne et al. (2013) for the Younger Dryas boundaries. If real, this asynchrony will most likely have affected interpretations of previous proxy alignments.

Asynchrony in key Holocene chronologies: Evidence from Irish bog pines

The Greenland Ice Core Chronology 2005 (GICC05) and the radiocarbon calibration curve (IntCal) are the foremost time scales used in paleoclimatic and paleoenvironmental studies of the most recent 10 k.y. Due to varying and often insufficient dating resolution, opportunities to test the synchrony of these two influential chronologies are rare. Here we present evidence for a phase of major pine recruitment on Irish bogs at ca. 8160 yr B.P. Dendrochronological dating of subfossil trees from three sites reveals synchronicity in germination across the study area, indicative of a regional forcing. The concurrent colonization of pine on peatland is interpreted in terms of drier surface conditions and provides the first substantive proxy data in support of a significant hydroclimatic change in the north of Ireland accompanying the 8.2 ka climate cooling event. The date of pine establishment does not overlap with the GICC05 age range for the event, and possible lags between responses are unlikely to explain the full difference. In light of recent studies highlighting a possible offset in GICC05 and IntCal dates, the Irish pine record supports the notion of ice core dates being too early during the period of study. If the suggested discrepancy in timing is an artifact of chronological error, it is likely to have affected interpretations of previous proxy comparisons and alignments.

Trophic Level Asynchrony in Rates of Phenological Change For Marine, Freshwater and Terrestrial Environments

Recent changes in the seasonal timing (phenology) of familiar biological events have been one of the most conspicuous signs of climate change. However, the lack of a standardised approach to analysing change has hampered assessment of consistency in such changes among different taxa and trophic levels and across freshwater, terrestrial and marine environments. We present a standardised assessment of 25 532 rates of phenological change for 726 UK terrestrial, freshwater and marine taxa. The majority of spring and summer events have advanced, and more rapidly than previously documented. Such consistency is indicative of shared large-scale drivers. Furthermore, average rates of change have accelerated in a way that is consistent with observed warming trends. Less coherent patterns in some groups of organisms point to the agency of more local scale processes and multiple drivers. For the first time we show a broad scale signal of differential phenological change among trophic levels; across environments advances in timing were slowest for secondary consumers, thus heightening the potential risk of temporal mismatch in key trophic interactions. If current patterns and rates of phenological change are indicative of future trends, future climate warming may exacerbate trophic mismatching, further disrupting the functioning, persistence and resilience of many ecosystems and having a major impact on ecosystem services

Experimental evidence for the influence of food availability on incubation attendance and hatching asynchrony in the Australian reed warbler Acrocephalus australis

The amount of time a bird allocates to incubation is likely to be limited by energetic constraints. If food is abundant, energetic constraints may be reduced and the time spent incubating (incubation attendance) may increase. Moreover, the onset of incubation in relation to clutch completion may be advanced, resulting in a higher degree of hatching asynchrony. We measured the effect of experimentally increased food availability on incubation attendance and an estimate of hatching asynchrony in the Australian reed warbler Acrocephalus australis. Supplementary food was provided every other day, from a few days before the start of egg laying until just prior to hatching. Incubation attendance was measured with temperature loggers at nests receiving supplementary food and control nests. Hatching asynchrony was inferred from mass and size differences between siblings shortly after hatching. We found that 1) food supplementation resulted in an increase in incubation attendance, when comparing both nests receiving supplementary food to control nests as well as feeding to non-feeding days in nests receiving supplementary food, and 2) food supplementation resulted in a greater hatching asynchrony, without affecting clutch size, average egg volume or the likelihood of eggs hatching. This suggests that food availability acts in a proximate way to modify the extent of incubation attendance and hatching asynchrony. We discuss the adaptive significance of increased incubation attendance and a shift in the degree of hatching asynchrony in relation to food availability.

Asynchrony and regional differences in the reproductive cycle of the greenback stingaree Urolophus viridis from south-eastern Australia

Determining the periodicity of the reproductive cycle in chondrichthyan species when the population is recruiting asynchronously, as found for Urolopus viridis, can be problematic. The reproductive cycle generally requires distinguishable trends in reproductive indices across the population. The present study utilised other similar and sympatric urolophid species with synchronous reproductive cycles. Through data collected in the present study and comparisons of maximum total length (TL), periodicity of egg and embryo in utero, ovarian cycles, largest ovarian follicle diameter, and matrotrophic contribution (percentage increase from egg to embryo after maternal histotroph supplement) from similar studies, an annual reproductive cycle can be hypothesised. Sampling across two separate regions of Lakes Entrance (LE) and Western Bass Strait (WBS), U. viridis also showed regionality in several of the reproductive indices. Maximum TL and mass for females, mean size-at-birth, and female size-at-maturity and size-at-maternity in LE were markedly smaller than in WBS. In both regions litter size (1–2) increased with TL, with an exception of one female in WBS producing a litter of 3 which could be attributed to the larger TL. The implication of U. viridis producing such few young annually is they have the lowest biological productivity of any urolophid species in south-eastern Australia.

Land use imperils plant and animal community stability through changes in asynchrony rather than diversity

Human land use may detrimentally affect biodiversity, yet long-term stability of species communities is vital for maintaining ecosystem functioning. Community stability can be achieved by higher species diversity (portfolio effect), higher asynchrony across species (insurance hypothesis) and higher abundance of populations. However, the relative importance of these stabilizing pathways and whether they interact with land use in real-world ecosystems is unknown. We monitored inter-annual fluctuations of 2,671 plant, arthropod, bird and bat species in 300 sites from three regions. Arthropods show 2.0-fold and birds 3.7-fold higher community fluctuations in grasslands than in forests, suggesting a negative impact of forest conversion. Land-use intensity in forests has a negative net impact on stability of bats and in grasslands on birds. Our findings demonstrate that asynchrony across species—much more than species diversity alone—is the main driver of variation in stability across sites and requires more attention in sustainable management.

Effects of reflex stimulus intensity and stimulus onset asynchrony on prepulse inhibition and perceived intensity of the blink-eliciting stimulus

Prepulse inhibition of the blink reflex is widely applied to investigate information processing deficits in schizophrenia and other psychiatric patient groups. The present experiment investigated the hypothesis that prepulse inhibition reflects a transient process that protects preattentive processing of the prepulse. Participants were presented with pairs of blinkeliciting noises, some preceded by a prepulse at a variable stimulus onset asynchrony (SOA), and were asked to rate the intensity of the second noise relative to the first. Inhibition of blink amplitude was greater for a 110-dB (A) noise than for a 95-dB(A) noise with a 120-ms SOA, whereas there was no difference with a 30-ms SOA. The perceived intensity was also lower for the 110-dB(A) noise than for the 95-dB(A) noise with the 120-ms SOA, but not with the 30-ms SOA. The parallel results support a relationship between prepulse inhibition of response amplitude and perceived intensity. However, the prepulse did not reduce intensity ratings relative to control trials in some conditions, suggesting that prepulse inhibition is not always associated with an attenuation of the perceived impact of the blink-eliciting stimulus.

Wideband inhibition modulates the effect of onset asynchrony as a grouping cue

Onset asynchrony is arguably the most powerful grouping cue for the separation of temporally overlapping sounds (see Bregman 1990). A component that begins only 30–50 ms before the others makes a greatly reduced contribution to the timbre of a complex tone, or to the phonetic quality of a vowel (e.g. Darwin 1984). This effect of onset asynchrony does not necessarily imply a cognitive grouping process; instead it may result from peripheral adaptation in the response to the leading component in the few tens of milliseconds before the other components begin (e.g., Westerman and Smith 1984). However, two findings suggest that the effect of onset asynchrony cannot be explained entirely by peripheral adaptation. First, though the effect is smaller, the contribution of a component to the phonetic quality of a short-duration vowel is reduced when it ends after the other components (Darwin and Sutherland 1984; Roberts and Moore 1991).

Contralateral influences of wideband inhibition on the effect of onset asynchrony as a cue for auditory grouping

Onset asynchrony is an important cue for segregating sound mixtures. A harmonic of a vowel that begins before the other components contributes less to vowel quality. This asynchrony effect can be partly reversed by accompanying the leading portion of the harmonic with an octave-higher captor tone. The original interpretation was that the captor and leading portion formed a perceptual group, but it has recently been shown that the captor effect depends on neither a common onset time nor harmonic relations with the leading portion. Instead, it has been proposed that the captor effect depends on wideband inhibition in the central auditory system. Physiological evidence suggests that such inhibition occurs both within and across ears. Experiment 1 compared the efficacy of a pure-tone captor presented in the same or opposite ear to the vowel and leading harmonic. Contralateral presentation was at least as effective as ipsilateral presentation. Experiment 2 used multicomponent captors in a more comprehensive evaluation of harmonic influences on captor efficacy. Three captors with different fundamental frequencies were used, one of which formed a consecutive harmonic series with the leading harmonic. All captors were equally effective, irrespective of the harmonic relationship. These findings support and refine the inhibitory account. © 2007 Acoustical Society of America.

Inhibitory influences on asynchrony as a cue for auditory segregation

A harmonic that begins before the other harmonics contributes less than they do to vowel quality. This reduction can be partly reversed by accompanying the leading portion with a captor tone. This effect is usually interpreted as reflecting perceptual grouping of the captor with the leading portion. Instead, it has recently been proposed that the captor effect depends on broadband inhibition within the central auditory system. A test of psychophysical predictions based on this proposal showed that captor efficacy is (a) maintained for noise-band captors, (b) absent when a captor accompanies a harmonic that continues after the vowel, and (c) maintained for 80 ms or more over a gap between captor offset and vowel onset. These findings support and refine the inhibitory account. PsycINFO Database Record © 2006 APA, all rights reserved.