Odor of achlorophyllous plants' seeds drives seed-dispersing ants

Seed dispersal by ants is an important means of migration for plants. Although many 34 myrmecochorous plants have seeds containing elaiosome, a nutritional reward for ants, some 35 non-myrmecochorous seeds without elaiosomes are also dispersed by ant species. However, the 36 mechanism by which seeds without elaiosomes enable efficient dispersal by ants is scarcely 37 investigated. The seeds of the achlorophyllous and myco-heterotrophic herbaceous plant 38 Monotropastrum humile are very small without elaiosomes and require a fungal host for 39 germination and survival. We performed a bioassay using seeds of M. humile and the ant 40 Nylanderia flavipes to demonstrate ant-mediated seed dispersal. We also analyzed the volatile 41 odors emitted from M. humile seeds and conducted bioassays using dummy seeds coated with 42 seed volatiles. Although elaiosomes were absent from the M. humile seeds, the ants carried the 43 seeds to their nests. They also carried the dummy seeds coated with the seed volatile mixture to 44 the nest, and left some dummy seeds inside the nest and discarded the rest of the dummy seeds 45 outside the nest with a bias toward locations with moisture conditions, which might be 46 conducive to germination. We concluded that seeds of M. humile were dispersed by the ants, 47 and that seed odors were sufficient to induce directed dispersal even without elaiosomes. It is 48 probable that the fleshy fruit producing genus Monotropastrum evolved from the related 49 anemochorous genus Monotropa, which produces capsule fruit. This transformation from 50 anemochory to myrmecochory presents a novel evolutionary pathway toward ant-mediated seed 51 dispersal in an achlorophyllous plant.

Analysis of coastal-plain fluvial architecture and high-frequency stacking patterns in the Upper Cretaceous Masuk Formation, Utah, U.S.A.: Climate-driven cyclicity?

ABSTRACT Most sequence stratigraphic models are based on the premise that relative changes in sea level (RSL) control stacking patterns in continental-margin settings. An alternative hypothesis, however, is that upstream factors, notably variations in relative water discharge (RQW) or the ratio of water to sediment discharge can influence or control stratal stacking patterns in fluvial systems. Sequence boundaries of RQW-driven systems differ from those driven by base-level fluctuations in that: 1) the depth of incision increases updip, and 2) rates of erosion are spatially uniform, leading to the formation of widespread, planar sequence boundaries. This paper presents an architectural and stratigraphic analysis of the well-exposed Masuk Formation of the Henry Mountains Syncline in southern Utah, an Upper Cretaceous coastal-plain fluvial succession that is interpreted to have been influenced significantly by RQW. Six lithofacies are recognized, three (Facies 1–3) recording floodbasin, mire, and (in one short interval) estuarine environments, and three (Facies 4–6) record different kinds of channel fills on a coastal alluvial plain. Seven major composite channel bodies (Facies 4–6), separated by intervals of non-channel deposits (Facies 1–3), are recognized in the stratigraphic interval. Composite channel bodies display planar, sheet-like geometry and are laterally continuous to a significantly greater extent (> 10 km) than would be expected from purely autogenic channel-belt construction. Together, these intervals record a series of high-frequency sequences, formed along the western margin of the Western Interior Seaway. In each individual sequence is a repetitive facies succession from a basal chaotic sandstone with admixed mudrock and sandstone transitioning upward to a more organized cross-bedded and stratified sandstone. This is interpreted to record cyclical changes from a peaked (flashy) discharge regime to a more normal runoff regime. Paleoflow data indicate a dominance of transverse (eastward-directed) dispersal early in the accumulation of the Masuk Formation, shifting to a pattern of greater axial (northward) dispersal over time. The RQW signal is strong in the lower part of the formation, decreasing upward. This suggests that the relatively short-headed streams draining from the rising Sevier fold–thrust belt were strongly influenced by climatic cyclicity, whereas more distally sourced systems were not. This study provides new insights into the architecture and stacking patterns of coastal-plain fluvial successions, emphasizing the plausible role that climate can play in shaping alluvial architecture in the rock record.

Dispersal of semi-fleshy fruits to rock crevices by a rock-restricted rodent

Seed dispersal allows successive generations of plants to be mobile in space and time. Heeria argentea’s unusual fruit and its ubiquity in extremely rocky habitats, suggests that this tree requires a specialist disperser. We therefore investigated the dispersal ecology of H. argentea and Hartogiella schinoides. We found M. namaquensis rapidly removed H. argentea and H. schinoides fruits, moving them short distances within and between rock outcrops, and consumed only the pericarps. Birds were observed consuming H. schinoides, but not H. argentea fruits, suggesting M. namaquensis is its sole, specialist disperser. Most H. argentea seeds (65%) with removed pericarps germinated successfully, while intact fruits did not. We show rock outcrops represent fire refugia, allowing H. argentea trees to grow to large sizes, with small stems and a co-occurring, wind-dispersed tree, Widdringtonia nodiflora found away from these sites. This rodent–tree mutualism is perhaps the clearest global example of directed dispersal and shows that these endemic trees are highly adapted for survival in the southwestern Cape habitat and are not tropical relicts.

Landward-directed Dispersal of Benthic Foraminiferal Propagules At Two Shallow-water Sites in the Doboy Sound Area (Georgia, U.S.A.)

Transport of foraminiferal propagules is an important mode of dispersal in benthic foraminifera. Known to occur from tidal marshes and estuaries to deep-water environments, the former are particularly vulnerable to ongoing climate change. Because rising sea levels can have profound implications on local salinity and associated faunal compositions, transport of foraminiferal propagules within these environments can be crucial for local assemblages to respond to changing conditions. Here we focus on a shallow-water environment in southeastern Georgia to evaluate whether propagule transport occurs evenly or whether it shows a predominant direction, such as land- or seaward. Two sites were sampled in the Doboy Sound area: the southern tip of Sapelo Island and a site on the North River located approximately 10 km inland. We applied the propagule method using the fine fraction of the sediments that contains the propagule bank. Experimental conditions in the laboratory included three temperatures (18, 24 and 30°C) and three salinities (15, 25 and 35) to simulate a range of environments that might trigger the growth of various foraminiferal species. While adult in situ assemblages of both sites were at least partly influenced by the adjacent salt marshes, experimentally grown assemblages were dominated by mudflat, estuarine or more open marine species. Thus, propagule transport from the more terrestrial side of the assemblage gradient is limited, while propagules of more marine species can be transported far into the extensive estuarine system of the study area, where they can remain viable within the local propagule banks. Results provide important insights into possible changes in foraminiferal assemblages with rising sea-level on the Georgia coast.

Mollusk communities of the central Congo River shaped by combined effects of barriers, environmental gradients, and species dispersal

<p>Rapids, falls, and cascades might act as barriers for freshwater species, determining the species community up- and downstream of barriers. However, they affect community composition not only by acting as barriers but also by their influence on environmental gradients. Moreover, the directional dispersal of species along the watercourse might determine community composition. A suitable system to study these differential effects is the Congo River, the world’s second largest river by discharge. The small ‘Upper Congo Rapids’ ecoregion features several rapids known as barrier for fishes. The Wagenia Cataracts at the town of Kisangani constitute the strongest drop of the Congo River and several studies have emphasized its role as barrier for fish distribution. Alternative explanations for this pattern, however, are rarely evaluated. Though mollusks represent a vital component of the macrozoobenthos, with distribution patterns and underlying drivers often distinct from that of fishes, virtually no field surveys of the Congo River have been reported for decades. We collected and determined mollusks of 51 stations, recorded environmental conditions, and generated proxies for directional species dispersal and an indirect barrier effect. Those variables were subjected to distance-based redundancy analyses and variation partitioning in order to test whether the mollusk community compositions are better explained by an individual or combined influence of the direct and indirect effect of the cataract barrier, environmental conditions, and downstream-directed dispersal. Our survey showed an exclusive upstream/downstream distribution for just four out of the 19 species, suggesting a limited barrier effect. We revealed no direct influence of the barrier itself on community composition but of substrate type. However, we found an indirect effect of the barrier through replacing spatially structured communities upstream of the cataract with more uniform ones downstream. Downstream‑directed dispersal explained the highest fraction of variation in mollusk communities. Thus, environmental factors, the indirect cataract effect, and downstream-directed spatial proxies model mollusk community composition in concert. These results support previous studies showing a multi-factorial imprint on communities. However, a large fraction of variation community composition remained unexplained, potentially due to flood plain dynamics that (re-)shape mollusk communities constantly and a high temporal turnover, evidenced by the comparison with historical surveys. This is likely caused by the growth of Kisangani and resulting human activities. A monitoring system could allow better assessments of these impacts on communities and the conservation status of endemic species in the Wagenia Cataracts.</p>