On the mechanisms involved in biological heme crystallization

Blood-feeding organisms digest hemoglobin, releasing large quantities of heme inside their digestive tracts. Free heme is very toxic, and these organisms have evolved several mechanisms to protect against its deleterious effects. One of these adaptations is the crystallization of heme into the dark-brown pigment hemozoin (Hz). Here we review the process of Hz formation, focusing on organisms other than Plasmodium that have contributed to a better understanding of heme crystallization. Hemozoin has been found in several distinct classes of organisms including protozoa, helminths and insects and Hz formation is the predominant form of heme detoxification. The available evidence indicates that amphiphilic structures such as phospholipid membranes and lipid droplets accompanied by specific proteins play a major role in heme crystallization. Because this process is specific to a number of blood-feeding organisms and absent in their hosts, Hz formation is an attractive target for the development of novel drugs to control illnesses associated with these hematophagous organisms.     

The evolution of insect/vertebrate associations

The evolution of close vertebrate associations has occurred in seven orders of insects, resulting in a great diversity of interactions which range from commensalism to true parasitism. The evolution of each taxon of vertebrate associates is discussed in turn, some new ideas on the development of certain groups are presented and, on a broader scale, a general model for the evolution of ectoparasitic insects is proposed. It argues that all vertebrate associates have evolved along one of two macroevolutionary pathways which differ only in the sequencing of adaptations facilitating host association and host feeding. These pathways lead to parasite types which differ greatly in their life history and intimacy of host association.
Some microevolutionary processes influencing the diversification of ectoparasites are discussed, in particular the process of insect/vertebrate coevolution and the forms this may take. Host specificity, one consequence of coevolution, is recognised as an important factor influencing the structure of ectoparasite communities, and a hypothesis is presented that competition between ectoparasite species, mediated by host defensive responses, is also important in determining community structure.     

Adaptation of ticks to a blood-feeding environment: evolution from a functional perspective

Ticks had to adapt to an existing and complex vertebrate hemostatic system from being free-living scavengers. A large array of anti-hemostatic mechanisms evolved during this process and includes blood coagulation as well as platelet aggregation inhibitors. Several questions regarding tick evolution exist. What was the nature of the ancestral tick? When did ticks evolve blood-feeding capabilities? How did these capabilities evolve? Did host specificity influence the adaptation of ticks to a blood-feeding environment? What are the implications of tick evolution for future research into tick biology and vaccine development? We investigate these questions in the light of recent research into protein superfamilies from tick saliva. Our conclusions are that the main tick families adapted independently to a blood-feeding environment. This is supported by major differences observed in all processes involved with blood-feeding for hard and soft ticks. Gene duplication events played a major role in the evolution of novel protein functions involved in tick-host interactions. This occurred during the late Cretaceous and was stimulated by the radiation of birds and placental mammals, which provided numerous new niches for ticks to adapt to a new lifestyle. Independent adaptation of the main tick families to a blood-feeding environment has several implications for future tick research in terms of tick genome projects and vaccine development.     

Parasite transmission by insects: a female affair?

Understanding the relationship between the gender of insects and their ability to act as vectors of insect-borne diseases (IBDs) could provide clues as to the origin of the intimate interplay among insect, pathogen and vertebrate hosts. The vector activity of several species of blood-feeding insects is linked to adult females. Interestingly, the only known exception is the transmission of canine and human thelaziosis by a male dipteran fly. This biological difference raises the question as to whether the parasitic behaviour of male and female insects transmitting IBDs is an expression of a co-evolution of vectors and pathogens.     

Sn-protoporphyrin inhibits both heme degradation and hemozoin formation in Rhodnius prolixus midgut

Hematophagy is a feeding habit that involves the ingestion of huge amounts of heme. The hematophagous hemipteran Rhodnius prolixus evolved many genetic resources to protect cells against heme toxicity. The primary barrier against the deleterious effects of heme is the aggregation of heme into hemozoin in the midgut lumen. Hemozoin formation is followed by the enzymatic degradation of heme by means of a unique pathway whose end product is dicysteinyl-biliverdin IX-γ (Rhodnius prolixus biliverdin, RpBv). These mechanisms are complemented by a heme-binding protein (RHBP) in the hemolymph that attenuates the pro-oxidant effects of heme. In this work, we show that when insects are fed with blood enriched with a heme analog, Sn-protoporphyrin (SnPP-IX), both hemozoin synthesis and RpBv production are inhibited in a dose-dependent manner. These effects are accompanied by increased oxidative damage to the midgut epithelium and inhibition of oviposition, indicating that hemozoin formation and heme degradation are protective mechanisms that work together and contributed to the adaptation of this insect to successfully feed on vertebrate blood.     

Heme crystallization in the midgut of triatomine insects

Hemozoin (Hz) is a heme crystal produced by several blood-feeding organisms in order to detoxify free heme released upon hemoglobin (Hb) digestion. Here we show that heme crystallization also occurs in three species of triatomine insects. Ultraviolet-visible and infrared light absorption spectra of insoluble pigments isolated from the midgut of three triatomine species Triatoma infestans, Dipetalogaster maximus and Panstrongylus megistus indicated that all produce Hz. Morphological analysis of T. infestans and D. maximus midguts revealed the close association of Hz crystals to perimicrovillar membranes and also as multicrystalline assemblies, forming nearly spherical structures. Heme crystallization was promoted by isolated perimicrovillar membranes from all three species of triatomine bugs in vitro in heat-sensitive reactions. In conclusion, the data presented here indicate that Hz formation is an ancestral adaptation of Triatominae to a blood-sucking habit and that the presence of perimicrovillar membranes plays a central role in this process.     

A missing metabolic pathway in the cattle tick Boophilus microplus.

Heme proteins are involved in a wide variety of biological reactions, including respiration, oxygen transport and oxygen metabolism [1]. The heme prosthetic group is synthesized in almost all living organisms except for a few pathogenic bacteria and trypanosomatids that use blood as food [2] [3]. There is a general belief that all nucleated animal cells synthesize heme [1] [4]. However, blood-feeding arthropods ingest enormous amounts of vertebrate blood in a single meal and the heme pathway has not been studied in these animals. We have examined heme synthesis in two hematophagous arthropods - the blood-sucking bug Rhodnius prolixus and the cattle tick Boophilus microplus. We show that R. prolixus makes heme and has a fully operative heme biosynthetic pathway, while B. microplus does not. To our knowledge, this is the first report of an animal that does not synthesize its own heme and relies solely on the recovery of heme present in the diet. Because of the inability of Boophilus to synthesize heme and its ability to deal efficiently with large amounts of free heme, we propose this organism as a good model for studying heme transport and reutilization in animal cells.     

Horizontal transmission of the insect symbiont Rickettsia is plant-mediated

Bacteria in the genus Rickettsia, best known as vertebrate pathogens vectored by blood-feeding arthropods, can also be found in phytophagous insects. The presence of closely related bacterial symbionts in evolutionarily distant arthropod hosts presupposes a means of horizontal transmission, but no mechanism for this transmission has been described. Using a combination of experiments with live insects, molecular analyses and microscopy, we found that Rickettsia were transferred from an insect host (the whitefly Bemisia tabaci) to a plant, moved inside the phloem, and could be acquired by other whiteflies. In one experiment, Rickettsia was transferred from the whitefly host to leaves of cotton, basil and black nightshade, where the bacteria were restricted to the phloem cells of the plant. In another experiment, Rickettsia-free adult whiteflies, physically segregated but sharing a cotton leaf with Rickettsia-plus individuals, acquired the Rickettsia at a high rate. Plants can serve as a reservoir for horizontal transmission of Rickettsia, a mechanism which may explain the occurrence of phylogenetically similar symbionts among unrelated phytophagous insect species. This plant-mediated transmission route may also exist in other insect-symbiont systems and, since symbionts may play a critical role in the ecology and evolution of their hosts, serve as an immediate and powerful tool for accelerated evolution.     

Nuttalliella namaqua: a living fossil and closest relative to the ancestral tick lineage: implications for the evolution of blood-feeding in ticks

Ticks are monophyletic and composed of the hard (Ixodidae) and soft (Argasidae) tick families, as well as the Nuttalliellidae, a family with a single species, Nuttalliella namaqua. Significant biological differences in lifestyle strategies for hard and soft ticks suggest that various blood-feeding adaptations occurred after their divergence. The phylogenetic relationships between the tick families have not yet been resolved due to the lack of molecular data for N. namaqua. This tick possesses a pseudo-scutum and apical gnathostoma as observed for ixodids, has a leathery cuticle similar to argasids and has been considered the evolutionary missing link between the two families. Little knowledge exists with regard to its feeding biology or host preferences. Data on its biology and systematic relationship to the other tick families could therefore be crucial in understanding the evolution of blood-feeding behaviour in ticks. Live specimens were collected and blood meal analysis showed the presence of DNA for girdled lizards from the Cordylid family. Feeding of ticks on lizards showed that engorgement occurred rapidly, similar to argasids, but that blood meal concentration occurs via malpighian excretion of water. Phylogenetic analysis of the 18S nuclear and 16S mitochondrial genes indicate that N. namaqua grouped basal to the main tick families. The data supports the monophyly of all tick families and suggests the evolution of argasid-like blood-feeding behaviour in the ancestral tick lineage. Based on the data and considerations from literature we propose an origin for ticks in the Karoo basin of Gondwanaland during the late Permian. The nuttalliellid family almost became extinct during the End Permian event, leaving N. namaqua as the closest living relative to the ancestral tick lineage and the evolutionary missing link between the tick families.     

Transcriptional profile and differential fitness in a specialist milkweed insect across host plants varying in toxicity

Interactions between plants and herbivorous insects have been models for theories of specialization and co‐evolution for over a century. Phytochemicals govern many aspects of these interactions and have fostered the evolution of adaptations by insects to tolerate or even specialize on plant defensive chemistry. While genomic approaches are providing new insights into the genes and mechanisms insect specialists employ to tolerate plant secondary metabolites, open questions remain about the evolution and conservation of insect counterdefences, how insects respond to the diversity defences mounted by their host plants, and the costs and benefits of resistance and tolerance to plant defences in natural ecological communities. Using a milkweed‐specialist aphid (Aphis nerii) model, we test the effects of host plant species with increased toxicity, likely driven primarily by increased secondary metabolites, on aphid life history traits and whole‐body gene expression. We show that more toxic plant species have a negative effect on aphid development and lifetime fecundity. When feeding on more toxic host plants with higher levels of secondary metabolites, aphids regulate a narrow, targeted set of genes, including those involved in canonical detoxification processes (e.g., cytochrome P450s, hydrolases, UDP‐glucuronosyltransferases and ABC transporters). These results indicate that A. nerii marshal a variety of metabolic detoxification mechanisms to circumvent milkweed toxicity and facilitate host plant specialization, yet, despite these detoxification mechanisms, aphids experience reduced fitness when feeding on more toxic host plants. Disentangling how specialist insects respond to challenging host plants is a pivotal step in understanding the evolution of specialized diet breadths.     

Survey and host fitness effects of red-cockaded woodpecker blood parasites and nest cavity arthropods

Blood parasites and nest cavity arthropods associated with the red-cockaded woodpecker (Picoides borealis) were surveyed and the impact of blood-feeding arthropods on woodpecker fitness traits was assessed. Five woodpeckers (8%) were infected with unidentified microfilariae, and 1 woodpecker (2%) was infected with 2 species of haemoproteid (Haemoproteus velans and Haemoproteus borgesi). This is the first record of haemoproteids in this species and the first observation of H. borgesi in North America. We collected representatives of at least 6 families of mites and 12 families of primarily commensal insects from woodpecker cavities. Only a few specimens of blood-feeding insects were recovered. The mite Androlaelaps casalis was the most common hematophagous arthropod (prevalence = 76%, mean density = 51+/-7 mites/cavity). The number of A. casalis mites increased with cavity age but there was no association between the number of mites and the number of woodpecker eggs laid or the number of hatchlings or fledglings. In conclusion, the prevalence of blood parasites in the red-cockaded woodpecker is low, woodpecker cavities are not heavily infested with blood-feeding insects, and there is no evidence that A. casalis mites affect woodpecker fitness.     

Cooperative Blood-feeding and the Function and Implications of Feeding Aggregations in the Sand Fly,Lutzomyia longipalpis (Diptera: Psychodidae)

Given the importance that the evolution of cooperation bears in evolutionary biology and the social sciences, extensive theoretical work has focused on identifying conditions that promote cooperation among individuals. In insects, cooperative or altruistic interactions typically occur amongst social insects and are thus explained by kin selection. Here we provide evidence that in Lutzomia longipalpis, a small biting fly and an important vector of leishmaniasis in the New World, cooperative blood-feeding in groups of non-kin individuals results in a strong decrease in saliva expenditure. Feeding in groups also strongly affected the time taken to initiate a bloodmeal and its duration and ultimately resulted in greater fecundity. The benefits of feeding aggregations were particularly strong when flies fed on older hosts pre-exposed to sand fly bites, suggesting that flies feeding in groups may be better able to overcome their stronger immune response. These results demonstrate that, in L. longipalpis, feeding cooperatively maximizes the effects of salivary components injected into hosts to facilitate blood intake and to counteract the host immune defences. As a result, cooperating sand flies enjoy enormous fitness gains. This constitutes, to our knowledge, the first functional explanation for feeding aggregations in this species and potentially in other hematophagous insects and a rare example of cooperation amongst individuals of a non-social insects species. The evolution of cooperative group feeding in sand flies may have important implications for the epidemiology of leishmaniasis.     

Comparative analyses suggest that information transfer promoted sociality in male bats in the temperate zone

The evolution of sociality is a central theme in evolutionary biology. The vast majority of bats are social, which has been explained in terms of the benefits of communal breeding. However, the causes for segregated male groups remain unknown. In a comparative study, we tested whether diet and morphological adaptations to specific foraging styles, two factors known to influence the occurrence of information transfer, can predict male sociality. Our results suggest that the species most likely to benefit from information transfer--namely, those preying on ephemeral insects and with morphological adaptations to feeding in open habitat--are more likely to form male groups. Our findings also indicate that solitary life was the ancestral state of males and sociality evolved in several lineages. Beyond their significance for explaining the existence of male groups in bats, our findings highlight the importance of information transfer in the evolution of animal sociality.     

Perimicrovillar membranes promote hemozoin formation into Rhodnius prolixus midgut

Rhodnius prolixus is a hematophagous insect that ingests large quantities of blood in each blood-feeding session. This ingested blood provides important nutrients to sustain the insect's oogenesis and metabolic pathways. During the digestive process, however, huge amounts of heme are generated as a consequence of the hemoglobin breakdown. Heme is an extremely dangerous molecule, since it can generate reactive oxygen species in the presence of oxygen that impair the normal metabolism of the insect. Part of the hemoglobin-derived heme can associate with the perimicrovillar membranes (PMM) in the gut lumen of R. prolixus; in this study we demonstrate the participation of the PMM in a heme detoxification process. These membranes were able to successfully induce heme aggregation into hemozoin (Hz). Heme aggregation was not dependent on the erythrocyte membranes, since the contribution of these membranes to the process was negligible, demonstrating that the ability to induce heme aggregation is a feature of the PMM, possibly representing a pre-adaptation of the hemipterans to feeding on blood.     

Functional and morphological diversity of sperm in Drosophila

Unlike mammals, where the males produce huge quantities of tiny spermatozoa, insects, and Drosophila in particular, exhibit a wide range of reproductive strategies. Sperm gigantism in Drosophila deviates from the rules that normally govern anisogamy, i.e. differences in the size and quantity of male and female gametes. Sperm gigantism has driven anatomical, physiological and cytological adaptations that affect the correlated evolution of the male and female reproductive systems, and has led to the evolution of a new structure, the roller, located between the testis and the seminal vesicle, and to sperm coiling to form pellets. The diversification of sperm strategy is investigated in the light of sexual selection processes that occur in the female genital tract after copulation. These processes, which bias paternity, result from interactions either between spermatozoa from different males, or between the spermatozoa and the environment within the female reproductive tract. In Drosophila, increased sperm size does not confer any reproductive advantage on the male. The evolution of sperm gigantism does not seem to be attributable to competition between spermatozoa from different males, as has been shown to occur in some vertebrate species. Alternative mechanisms, such as interactions between spermatozoa and the female reproductive system, are therefore currently viewed as being more likely explanations. In particular, the impact of sperm size on female reproductive physiology is being investigated to find out whether having large spermatozoa increases the likelihood of male reproductive success. Correlated adaptations of the spermatozoa and female storage organs also seem to be a major factor in determining sperm success, and their role in male-female conflicts is discussed briefly.     

Evolution of nectarivory in phyllostomid bats (Phyllostomidae Gray, 1825, Chiroptera: Mammalia)

Background  

Bats of the family Phyllostomidae show a unique diversity in feeding specializations. This taxon includes species that are highly specialized on insects, blood, small vertebrates, fruits or nectar, and pollen. Feeding specialization is accompanied by morphological, physiological and behavioural adaptations. Several attempts were made to resolve the phylogenetic relationships within this family in order to reconstruct the evolutionary transitions accompanied by nutritional specialization. Nevertheless, the evolution of nectarivory remained equivocal.     

吸血节肢动物唾液腺来源的抗止血物质

在采食脊椎动物血液能力的进化过程中,吸血节肢动物的唾液腺形成了丰富的抗止血因子,如血小板聚集抑制因子,他们通过不同机制抑制ADP、凝血酶和胶原等诱导的血小板聚集.抗凝因子能扰乱内源性和外源性止血通路.血管扩张因子包括储藏、运输一氧化氮的nitrophorins,模拟内源性血管扩张的多肽和催化或水解内源性血管收缩因子的酶.吸血节肢动物的唾液腺蛋白可以通过直接作用或协同作用起到抗止血的效果.复杂多样的唾液腺生物活性分子解释了吸血节肢动物成功获得血餐的分子机制,也提供了新的抗止血药物分子.     

Evolution of the salivary apyrases of blood-feeding arthropods

Phylogenetic analyses of three families of arthropod apyrases were used to reconstruct the evolutionary relationships of salivary-expressed apyrases, which have an anti-coagulant function in blood-feeding arthropods. Members of the 5′nucleotidase family were recruited for salivary expression in blood-feeding species at least five separate times in the history of arthropods, while members of the Cimex-type apyrase family have been recruited at least twice. In spite of these independent events of recruitment for salivary function, neither of these families showed evidence of convergent amino acid sequence evolution in salivary-expressed members. On the contrary, in the 5′-nucleotide family, salivary-expressed proteins conserved ancestral amino acid residues to a significantly greater extent than related proteins without salivary function, implying parallel evolution by conservation of ancestral characters. This unusual pattern of sequence evolution suggests the hypothesis that purifying selection favoring conservation of ancestral residues is particularly strong in salivary-expressed members of the 5′-nucleotidase family of arthropods because of constraints arising from expression within the vertebrate host.     

Vampires,Pasteur and reactive oxygen species. Is the switch from aerobic to anaerobic metabolism a preventive antioxidant defence in blood-feeding parasites?

Several species of parasites show a reduction of their respiratory activity along their developmental cycles after they start to feed on vertebrate blood, relying on anaerobic degradation of carbohydrates to achieve their energy requirements. Usually, these parasites choose not to breathe despite of living in an environment of high oxygen availability such as vertebrate blood. Absence of the 'Pasteur effect' in most of these parasites has been well documented. Interestingly, together with the switch from aerobic to anaerobic metabolism in these parasites, there is clear evidence pointing to an increase in their antioxidant defences. As the respiratory chain in mitochondria is a major site of production of reactive oxygen species (ROS), we propose here that the arrest of respiration constitutes an adaptation to avoid the toxic effects of ROS. This situation would be especially critical for blood-feeding parasites because ROS produced in mitochondria would interact with pro-oxidant products of blood digestion, such as haem and/or iron, and increase the oxidative damage to the parasite's cells.     

Patterning with clocks and genetic cascades: Segmentation and regionalization of vertebrate versus insect body plans

Oscillatory and sequential processes have been implicated in the spatial patterning of many embryonic tissues. For example, molecular clocks delimit segmental boundaries in vertebrates and insects and mediate lateral root formation in plants, whereas sequential gene activities are involved in the specification of regional identities of insect neuroblasts, vertebrate neural tube, vertebrate limb, and insect and vertebrate body axes. These processes take place in various tissues and organisms, and, hence, raise the question of what common themes and strategies they share. In this article, we review 2 processes that rely on the spatial regulation of periodic and sequential gene activities: segmentation and regionalization of the anterior–posterior (AP) axis of animal body plans. We study these processes in species that belong to 2 different phyla: vertebrates and insects. By contrasting 2 different processes (segmentation and regionalization) in species that belong to 2 distantly related phyla (arthropods and vertebrates), we elucidate the deep logic of patterning by oscillatory and sequential gene activities. Furthermore, in some of these organisms (e.g., the fruit fly Drosophila), a mode of AP patterning has evolved that seems not to overtly rely on oscillations or sequential gene activities, providing an opportunity to study the evolution of pattern formation mechanisms.