Commensal vs. parasitic relationship between Carapini fish and their hosts: some further insight through δC and δN measurements

In the Moorea Lagoon (French Polynesia), the pearlfish Carapus boraborensis, Carapus homei, Carapus mourlani and Encheliophis gracilis are generally found inside echinoderm hosts such as the holothurian Bohadschia argus and the starfish Culcita novaeguineae. At the end of their larval stage, these fish settle on the reef and directly enter their echinoderm host where they undergo an important metamorphosis. The aim of this study was to get further insight on the type of symbiosis (commensal vs. parasite) between these fish and their hosts. δ¹⁵N and δ¹³C measurements were determined in the tissues of invertebrate hosts (holothurians and starfish) and carapids (larvae, juveniles and adults). The obtained isotopic signatures reveal different kinds of associations: metamorphosing larvae, juveniles and adults of C. boraborensis and C. homei do not feed at all on host holothurian tissues, C. mourlani and its asterian host display a commensal relationship without any feeding association, while E. gracilis is likely to feed on the tissue of the holothurian.     

Do trematode parasites disrupt defence-cell signalling in their snail hosts?

More than a decade ago, it was postulated that components derived from trematode parasites block receptors on the defence cells of their snail intermediate hosts, thus preventing host-cell activation and parasite elimination. This phenomenon has still not been investigated extensively. However, recent work concerning the molecular regulation of the molluscan defence response provides a new framework for studies that focus on an extension of this original concept - subversion of host cell signalling by trematode parasites. The hypothesis is that, to facilitate survival and replication in their intermediate hosts, trematode parasites down regulate host defence responses by interfering with key signal-transduction pathways in snail defence cells.     

Branchiobdellid annelids and their crayfish hosts: are they engaged in a cleaning symbiosis?

Branchiobdellid annelids and their freshwater crayfish hosts are generally thought to have a commensal relationship. Branchiobdellids of the genus Cambarincola exploit their hosts through a variety of mechanisms; however, an effect of branchiobdellids on crayfish has not been conclusively demonstrated. We investigated whether branchiobdellids positively affect the host crayfish Cambarus chasmodactylus in the New River, North Carolina. In a laboratory experiment, we placed 0, 3, or 6 branchiobdellids on C. chasmodactylus and observed a significant effect of branchiobdellid presence on both growth and mortality of host crayfish; crayfish with branchiobdellids exhibited faster growth and lower mortality with increasing branchiobdellid density. A tracer experiment demonstrated that branchiobdellids feed on items found in the branchial chamber of C. chasmodactylus. We hypothesize that such feeding activity by branchiobdellids reduces fouling of crayfish gills by epibionts and particulate matter and could lead to the reduced mortality and increased growth rates observed in the laboratory experiment. Specifically, Cambarincola may improve the ventilatory and excretory fitness of C. chasmodactylus by cleaning gill filaments. Field data support this hypothesis by demonstrating that branchiobdellids are found disproportionately at sites proximal to the branchial chamber in the New River. This study provides evidence that the relationship between C. chasmodactylus and Cambarincola may be a cleaning symbiosis, at least in environments where gill fouling is a problem for C. chasmodactylus.     

Kidney atrophy vs hypertrophy in diabetes: which cells are involved?

One of the first structural changes in diabetic nephropathy (DN) is the renal enlargement. These changes resulted in renal hypertrophy in both glomerular and tubular cells. Shrink in the kidney size, which described as kidney atrophy resulted from the loss of nephrons or abnormal nephron function and lead to loss of the kidney function. On the other hand, increase in kidney size, which described as hypertrophy resulted from increase in proximal tubular epithelial and glomerular cells size. However overtime, tubular atrophy and tubulointerstitial fibrosis occurs as subsequent changes in tubular cell hypertrophy, which is associated with the infiltration of fibroblast cells into the tubulointerstitial space. The rate of deterioration of kidney function shows a strong correlation with the degree of tubulointerstitial fibrosis. A consequence of long-standing diabetes/hyperglycemia may lead to major changes in renal structure that occur but not specific only to nephropathy. Identifying type of cells that involves in renal atrophy and hypertrophy may help to find a therapeutic target to treat diabetic nephropathy. In summary, the early changes in diabetic kidney are mainly includes the increase in tubular basement membrane thickening which lead to renal hypertrophy. On the other hand, only renal tubule is subjected to apoptosis, which is one of the characteristic morphologic changes in diabetic kidney to form tubular atrophy at the late stage of diabetes.     

Birds and their parasites: victims of infection or fashion?

Vilnius, Lithuania June 1998     

Phenological asynchrony between herbivorous insects and their hosts: signal of climate change or pre-existing adaptive strategy?

Climate change alters phenological relations between interacting species. We might expect the historical baseline, or starting-point, for such effects to be precise synchrony between the season at which a consumer most requires food and the time when its resources are most available. We synthesize evidence that synchrony was not the historical condition in two insect–plant interactions involving Edith''s checkerspot butterfly (Euphydryas editha), the winter moth (Operophtera brumata) and their host plants. Initial observations of phenological mismatch in both systems were made prior to the onset of anthropogenically driven climate change. Neither species can detect the phenology of its host plants with precision. In both species, evolution of life history has involved compromise between maximizing fecundity and minimizing mortality, with the outcome being superficially maladaptive strategies in which many, or even most, individuals die of starvation through poor synchrony with their host plants. Where phenological asynchrony or mismatch with resources forms the starting point for effects of anthropogenic global warming, consumers are particularly vulnerable to impacts that exacerbate the mismatch. This vulnerability likely contributed to extinction of a well-studied metapopulation of Edith''s checkerspot, and to the skewed geographical pattern of population extinctions underlying a northward and upward range shift in this species.     

When will rejection of parasite nestlings by hosts of nonevicting avian brood parasites be favored? A misimprinting-equilibrium model

It has been suggested that discrimination and rejection of thenestlings of avian brood parasites are most likely to evolvewhen the parasite nestling is raised alongside the host nestlings,for example, many cowbird-host systems. Under these circumstances,the benefits of discrimination are high because the host parentsmay save most of their brood. However, there is a general absenceof nestling rejection behavior among hosts of nonevicting parasites.In a cost-benefit equilibrium model, based on the premise thathost species learn to recognize their offspring through imprintingon first breeding, we show that nestling recognition can beadaptive for hosts of cowbirds, but only under strict conditions.Namely, when host nestling survival alongside the parasite islow, rates of parasitism are high and the average clutch sizeis large. All of these conditions are seldom simultaneouslyachieved in real systems. Most importantly, the parasite nestling,on average, does not sufficiently depress host nestling survivalto outweigh the costs of nestling recognition and rejectionerrors. Thus, we argue that nestling acceptance behaviors byhosts of nonevicting brood parasites may be explained as anevolutionary equilibrium in which recognition costs act as astabilizing selection pressure against rejection when most ofthe host's offspring survive parasitism.     

Evolution of trophic transmission in parasites: why add intermediate hosts?

Although multihost complex life cycles (CLCs) are common in several distantly related groups of parasites, their evolution remains poorly understood. In this article, we argue that under particular circumstances, adding a second host to a single-host life cycle is likely to enhance transmission (i.e., reaching the target host). For instance, in several situations, the propagules of a parasite exploiting a predator species will achieve a higher host-finding success by encysting in a prey of the target predator than by other dispersal modes. In such a case, selection should favor the transition from a single- to a two-host life cycle that includes the prey species as an intermediate host. We use an optimality model to explore this idea, and we discuss it in relation to dispersal strategies known among free-living species, especially animal dispersal. The model found that selection favored a complex life cycle only if intermediate hosts were more abundant than definitive hosts. The selective value of a complex life cycle increased with predation rates by definitive hosts on intermediate hosts. In exploring trade-offs between transmission strategies, we found that more costly trade-offs made it more difficult to evolve a CLC while less costly trade-offs between traits could favor a mixed strategy.     

Host switching in cowbird brood parasites: how often does it occur?

Avian obligate brood parasites lay their eggs in nests of host species, which provide all parental care. Brood parasites may be host specialists, if they use one or a few host species, or host generalists, if they parasitize many hosts. Within the latter, strains of host‐specific females might coexist. Although females preferentially parasitize one host, they may occasionally successfully parasitize the nest of another species. These host switching events allow the colonization of new hosts and the expansion of brood parasites into new areas. In this study, we analyse host switching in two parasitic cowbirds, the specialist screaming cowbird (Molothrus rufoaxillaris) and the generalist shiny cowbird (M. bonariensis), and compare the frequency of host switches between these species with different parasitism strategies. Contrary to expected, host switches did not occur more frequently in the generalist than in the specialist brood parasite. We also found that migration between hosts was asymmetrical in most cases and host switches towards one host were more recurrent than backwards, thus differing among hosts within the same species. This might depend on a combination of factors including the rate at which females lay eggs in nests of alternative hosts, fledging success of the chicks in this new host and their subsequent success in parasitizing it.     

Carcass maintenance and biparental brood care in burying beetles: are males redundant?

1. Burying beetles inter small vertebrate carcasses that ultimately serve as a food source for their developing young. The male remains with the female on the carcass after the brood has been produced, purportedly to aid in the feeding and protection of larvae. However, numerous laboratory experiments have failed to demonstrate a beneficial effect of the male on the growth and survival of offspring.
2. A potential difficulty with laboratory studies is that beetles are typically held under relatively benign conditions, protected from the biotic and environmental challenges that they normally encounter. In nature, males may enhance offspring survival by aiding the female in ridding the carcass of mould, and by helping to preserve the carcass through the secretion of antibiotic substances in the beetles' saliva. To examine more rigorously the potential benefits of male parental care, an experiment was conducted under field conditions in which the reproductive output of male–female pairs was compared to that of single females.
3. Beetles were induced to bury carcasses in soil inside rigid plastic tubes that had been inserted into the ground. The experiment was a paired design involving pairs of sisters reproducing in adjacent tubes; one sister reproduced alone, whereas the other reproduced with the assistance of a male. Soil cores were recovered about 1 month later, and examined for viable pupae.
4. There was no significant difference in the number of offspring produced by single females and those reproducing with the assistance of the male, nor was there any significant difference in total brood mass. These results suggest that any benefits of extended male residency on the carcass do not stem from male participation in carcass maintenance or provisioning young.     

Why some parasites are widespread and abundant while others are local and rare?

Abundances and distributions of species are usually associated. This implies that as a species declines in abundance so does the number of sites it occupies. Conversely, when there is an increase in a species' range size, it is usually followed by an increase in population size (Gaston et al. 2000 ). This ecological phenomenon, also known as the abundance–occupancy relationship (AOR), is well documented in several species of animals and plants (Gaston et al. 2000 ) but has been little investigated in parasites. In this issue of Molecular Ecology, Drovetski et al. ( 2014 ) investigated the AOR in avian haemosporidians (vector‐borne blood parasites) using data from four well‐sampled bird communities. In support of the AOR, the research group found that the abundance of parasite cytochrome b lineages (a commonly used proxy for species identification within this group of parasites) was positively linked with the abundance of susceptible avian host species and that the most abundant haemospordian lineages were those with larger ranges. Drovetski et al. ( 2014 ) also found evidence for both hypotheses proposed to explain the AOR in parasites: the trade‐off hypothesis (TOH) and the niche‐breadth hypothesis (NBH). Interestingly, the main predictor of the AOR was the number of susceptible hosts (i.e. number of infected birds) and not the number of host species the parasites were able to exploit.     

Gamma vs beta irradiation: which is superior?

Background. The debate over which radioisotope, gamma-emitting or beta-emitting, is ideal for vascular brachytherapy, is as old as the field itself. Gamma isotopes such as Ir-192 have been successfully used in large-scale clinical trials. However, radiation protection and safety remains a practical issue when high energy gamma rays are used in interventional suites.Methods. In this report, we have evaluated dosimetric properties of currently available radiation sources, gamma and beta, in terms of their utility in vascular brachytherapy. Published data have been analyzed in comparing the depth doses of these two radiation modalities.Results and Conclusions. Our evaluation shows that significant dosimetric differences do exist between gamma and beta sources. The superiority of one over the other in clinical utility will more likely be determined by the outcome of human trials.     

Ciliary subcompartments: how are they established and what are their functions?

Cilia are conserved subcellular organelles with diverse sensory and developmental roles. Recently, they have emerged as crucial organelles whose dysfunction causes a wide spectrum of disorders called ciliopathies. Recent studies on the pathological mechanisms underlying ciliopathies showed that the ciliary compartment is further divided into subdomains with specific roles in the biogenesis, maintenance and function of cilia. Several conserved sets of molecules that play specific roles in each subcompartment have been discovered. Here we review recent progress on our understanding of ciliary subcompartments, especially focusing on the molecules required for their structure and/or function. [BMB Reports 2015; 48(7): 380-387]     

The sixth mass coextinction: are most endangered species parasites and mutualists?

The effects of species declines and extinction on biotic interactions remain poorly understood. The loss of a species is expected to result in the loss of other species that depend on it (coextinction), leading to cascading effects across trophic levels. Such effects are likely to be most severe in mutualistic and parasitic interactions. Indeed, models suggest that coextinction may be the most common form of biodiversity loss. Paradoxically, few historical or contemporary coextinction events have actually been recorded. We review the current knowledge of coextinction by: (i) considering plausible explanations for the discrepancy between predicted and observed coextinction rates; (ii) exploring the potential consequences of coextinctions; (iii) discussing the interactions and synergies between coextinction and other drivers of species loss, particularly climate change; and (iv) suggesting the way forward for understanding the phenomenon of coextinction, which may well be the most insidious threat to global biodiversity.     

Genetic differentiation between two host “races” and two species of cleptoparasitic bees and between their two hosts

In this paper we test the following two hypotheses: (1) that apparently conspecific samples of the cleptoparasitic beeCoelioxys funeraria, differing markedly in size and reared from different host species, do indeed represent one panmictic population; (2) that bees that nest in holes in wood or twigs have higher levels of genetic variation than those nesting in the ground. Based upon 41 loci, the genetic differences between the two samples ofC. funeraria could be explained entirely in terms of sampling error. In contrast, the sympatricC. moesta showed 16 fixed allelic differences from theC. funeraria samples. Similarly, the two hosts ofC. funeraria, Megachile relativa andM. inermis, had 21 fixed allelic differences between them out of 42 presumptive gene loci. Heterozygosities among the wood-nesting bees were not particularly high for Hymenoptera, ranging from 0.045 to 0.054. Comparisons of heterozygosity estimates among bees remain ambiguous as to whether soil nesting confers sufficient environmental buffering effects to reduce possible advantages of heterosis in ground-nesting species.