ALBERT

Description: The various meanings of "competition" in ecology, genetics and evolution are grouped into four main meanings which differ in important respects from each other. They grade from a strict meaning to one so broad as to be synonymous with natural selection. In the strict sense competition between animals occurs when a number of animals (of the same or of different species) utilize common resources the supply of which is short; or if the resources are not in short supply competition occurs when the animals seeking that resource nevertheless harm one or another in the process. Intermediate between the strict and the broad meanings are two others. One includes any interference of one species by another irrespective of whether they use common resources or not, and the other includes predation within the meaning of competition. Each of the four meanings of competition is illustrated with examples. A distinction is made between the influence of one species on the numbers of another and the influence of one genotype on the frequency of another genotype of the same species. In the former case one species can influence the frequency of another by competition only when there is a shortage of some resource. The one exception is some special cases of threat. The conclusion is drawn that if the term competition is retained in biological writings it should be restricted to the one strict meaning defined above. On the other hand this may be an appropriate time for approaching the problems of how one organism influences the numbers of another in a fresh way without recourse to the concept of competition at all.

Description: The postcollisional tectonic development of northeast Mozambique and subsequent cooling from high-temperature metamorphism is delineated with an extensive new set of U-Pb titanite, 40Ar/39Ar hornblende, and 40Ar/39Ar mica analyses. The complex data suggest a polyphase metamorphic history from the late Neoproterozoic to the Ordovician within the East African–Antarctic Orogen (EAAO), with marked differences between the major constituent blocks. In all the data sets, samples from the basement south of the Lúrio Belt show generally younger ages than those from the north, resulting from a late metamorphic event and slow cooling between ca. 520 and 440 Ma. The ages north and south of the Lúrio Belt are consistently offset by ca. 30–70 Ma, a difference that is maintained and even appears to increase during cooling from very high temperatures to ca. 350°C. Based on the first-order assumption that all the ages are cooling ages, cooling rates in the south are estimated at ca. 7°–8°C/Ma, while those north of the Lúrio Belt are faster at ca. 16°C/Ma. The data are consistent with previous geochronological, petrographic, and field data and suggest a late high-temperature/low-pressure metamorphic event that affected only the basement rocks south of the Lúrio Belt and portions of the latter. This late metamorphism and subsequent delayed, slower cooling agree well with a model of elevated heat flow following lithosphere delamination in the southern part of the orogen, which also explains the observed widespread granitoid magmatism, migmatization, and renewed deformation in the southern basement.

Description: The dichotomy between high microbial abundance (HMA) and low microbial abundance (LMA) sponges has been long recognized. In the present study, 56 sponge species from three geographic regions (greater Caribbean, Mediterranean, Red Sea) were investigated by transmission electron microscopy for the presence of microorganisms in the mesohyl matrix. Additionally, bacterial enumeration by DAPI-counting was performed on a subset of samples. Of the 56 species investigated, 28 were identified as belonging to the HMA and 28 to the LMA category. The sponge orders Agelasida and Verongida consisted exclusively of HMA species, and the Poecilosclerida were composed only of LMA sponges. Other taxa contained both types of microbial associations (e.g., marine Haplosclerida, Homoscleromorpha, Dictyoceratida), and a clear phylogenetic pattern could not be identified. For a few sponge species, an intermediate microbial load was determined, and the microscopy data did not suffice to reliably determine HMA or LMA status. To experimentally determine the HMA or LMA status of a sponge species, we therefore recommend a combination of transmission electron microscopy and 16S rRNA gene sequence data. This study significantly expands previous reports on microbial abundances in sponge tissues and contributes to a better understanding of the HMA-LMA dichotomy in sponge-microbe symbioses.

Description: The mating behavior of deep-sea squids is shrouded in mystery. The squids for which mating has been observed use a hectocotylus, a modified arm, for the transfer of sperm packets called spermatophores. However, many deep-sea squid species lack a hectocotylus. We present the first in situ observations of mating behavior in a deep-sea squid that has no hectocotylus but instead uses an elongated terminal organ for the transfer of spermatangia, which are released from the spermatophores and burrow deeply into the female tissue. With remotely operated vehicles (ROVs), we observed two mating pairs of the deep-sea squid Pholidoteuthis adami in the Gulf of Mexico. The male adopted a peculiar position during mating, with its ventral side up and its posterior mantle above the female's head. While the male held the female in what looked like a firm grip, we observed the long terminal organ extending through the funnel of the male, contacting the female dorsal mantle. Examinations of museum specimens show that spermatangia burrow from the outer dorsal mantle into the inner dorsal mantle. This combination of serendipitous in situ observations and archived specimens can be a powerful tool for understanding the behavior of deep-sea animals.

Description: The evolution of reproductive isolation among populations is often the result of selective forces. Among those, parasites exert strong selection on host populations and can thus also potentially drive reproductive isolation. This hypothesis has yet to be explicitly tested, and here we set up a multigenerational coevolution experiment to explore this possibility. Five lines of Tribolium castaneum were allowed to coevolve with their natural parasite, Nosema whitei; five paired lines of identical origin were maintained in the absence of parasites. After 17 generations, we measured resistance within and reproductive isolation between all lines. Host lines from the coevolution treatment had considerably higher levels of resistance against N. whitei than their paired host lines, which were maintained in the absence of parasites. Reproductive isolation was greater in the coevolved selection regime and correlated with phenotypic differentiation in parasite resistance between coevolved host lines. This suggests the presence of a selection-driven genetic correlation between offspring number and resistance. Our results show that parasites can be a driving force in the evolution of reproductive isolation and thus potentially speciation.

Description: In vertebrates, maternal transfer of immunity via the eggs or the placenta provides offspring with crucial information on prevailing pathogens and parasites. Males contribute little to such trans-generational immune priming, either because they do not share the environment and parasite pressure of the offspring, or because sperm are suggested to be too small for transfer of immunity. In the teleost group of Syngnathids (pipefish, seahorses and sea dragons) males brood female eggs in a placenta-like structure. Such sex-role-reversed species provide a unique opportunity to test for adaptive plasticity in immune transfer. Here males in addition to females should influence offspring immunity. We experimentally tested paternal effects on offspring immunity by examining immune cell proliferation and immune gene expression. Maternal and paternal bacterial exposure induced the offspring's immune defence five weeks after hatching, and this effect persisted in four-month-old offspring. For several offspring immune traits double parental exposure (maternal and paternal) enhanced the response, while for another group of immune traits, the trans-generational induction already took place if only one parent was exposed. Our study shows that sex-role reversal in connection with male pregnancy opens the door for bi-parental influences on offspring immunity, and may represent one additional advantage for the evolution of male pregnancy.

Description: Since the mid-19th century biologists have considered the east tropical Pacific to be a barrier for the dispersal of coastal marine invertebrate species. More recently it has been maintained that this is so because planktonic larvae are unable to cross such a large expanse of ocean. Therefore, it seems extraordinary that no observations have been made to determine whether larvae of invertebrates are actually transported by the major currents of that region. Plankton samples in the present study show that invertebrate larvae do occur within the east tropical Pacific including, but not restricted to, those of gastropods, polychaetes, sipunculans, decapod crustacea, echinoderms, and coelenterates-though as a rule, their occurrence there is significantly less than within the central tropical Pacific. Data from larval distributions suggest that the east tropical Pacific may act as a substantial impediment to many invertebrate forms, but that it is not a complete barrier to dispersal. Accordingly, the region is best considered a filter. It allows only species with a potential for an exceptionally long larval life to pass i.e., those with teleplanic larvae, while it blocks other forms that are restricted to a shorter time in the plankton owing to an inability to delay metamorphosis or lack of an alternate mode of dispersal. The capacity for dispersal by planktonic larvae differs among the various taxa.

Description: The concept that diversity promotes reliability of ecosystem function depends on the pattern that community-level biomass shows lower temporal variability than species-level biomasses. However, this pattern is not universal, as it relies on compensatory or independent species dynamics. When in contrast within–trophic level synchronization occurs, variability of community biomass will approach population-level variability. Current knowledge fails to integrate how species richness, functional distance between species, and the relative importance of predation and competition combine to drive synchronization at different trophic levels. Here we clarify these mechanisms. Intense competition promotes compensatory dynamics in prey, but predators may at the same time increasingly synchronize, under increasing species richness and functional similarity. In contrast, predators and prey both show perfect synchronization under strong top-down control, which is promoted by a combination of low functional distance and high net growth potential of predators. Under such conditions, community-level biomass variability peaks, with major negative consequences for reliability of ecosystem function.

Description: The 18,500 yr. b.p. Cape Riva (CR) eruption of Santorini vented several km3 or more of magma, generating four eruption units: a basal Plinian fall deposit (CR-A) and three pyroclastic flow deposits (CR-B to CR-D upwards). CR-B and CR-D are welded ignimbrites; CR-C consists predominantly of up to 25 m thick coarse, lithic-rich co-ignimbrite lag breccias resulting from a climactic phase of the eruption. The initial Plinian phase occurred from a localized vent in N Santorini, and subsequent column collapse resulted in emplacement of CR-B. Towards the end of CR-B, new conduits were activated and pyroclastic flows discharged from multiple vents to generate the lag breccias (CR-C). CR-D probably records a return to a localized vent as the eruption waned. The eruption sampled a zoned magma chamber containing rhyodacite overlying andesite, and leaks of these magmas were manifested as the Skaros-Therasia lavas preceding the CR eruption. Plinian and initial ignimbrite stages occurred while the magma chamber was overpressured; subsequent underpressuring, due to magma discharge, caused fracturing of the chamber roof, caldera collapse, and eruption of pyroclastic flows from multiple vents. Activation and widening of new conduits during collapse resulted in the rapid escalation of discharge rate favoring the formation of lag breccias by: (i) promoting erosion of lithic debris at the surface vent; and (ii) raising surface exit pressures, thereby resulting in a dramatic increase in the grain size of the ejecta.