Facultative Host Research Articles

The Roles of Mosquitoes in the Circulation of Monoxenous Trypanosomatids in Temperate Climates.

Monoxenous (insect-restricted) trypanosomatids are highly diverse and abundant in nature. While many papers focus on the taxonomy and distribution of these parasites, studies on their biology are still scarce. In particular, this concerns trypanosomatids inhabiting the ubiquitous mosquitoes. To shed light on the circulation of monoxenous trypanosomatids with the participation of mosquitoes, we performed a multifaceted study combining the examination of naturally- and experimentally-infected insects using light and electron microscopy and molecular identification of parasites. Our examination of overwintering mosquitoes (genera Culex and Culiseta) revealed that their guts contained living trypanosomatids, which can be spread during the next season. Experimental infections with Crithidia spp. demonstrated that imagines represent permissive hosts, while larvae are resistant to these parasites. We argue that for the parasites with wide specificity, mosquitoes act as facultative hosts. Other trypanosomatids may have specific adaptations for vertical transmission in these insects at the expense of their potential to infect a wider range of hosts and, consequently, abundance in nature.

The Importance of Home Cleaning: Sediment Transport by Alpheid Shrimps Provides a Competitive Advantage to Their Host Anemones

Bartholomea annulata is a facultative host of the A. armatus species complex. In the Mexican Caribbean it is commonly found in cracks and crevices located where the vertical walls meet the sandy bottom or on large coral patches away from the sand. To protect themselves from predators, anemones often contract their hydraulic body into a cavernous den and extend the stinging tentacles toward the entrance. The high sediment dynamics of the region, however, result in a permanent risk of animal shelters to be obstructed by sand. By both analysing field data and conducting laboratory experiments with artificial shelters, the present study explored the den cleaning behaviour widely extended amongst alpheid shrimp, and its role in the alpheid-anemone symbiotic interaction. Videorecordings showed that den cleaning was composed of three main behaviours: digging, tossing and tamping. It commenced as soon as 7.2 ± 10.5 min after anemones were recognised by alpheids, and behaviours were displayed systematically amongst all 12 replicates. Despite being completely burrowed in sand, Alpheus spp. were capable of finding the anemone and liberating the entrance of the artificial shelters in less than 2.5 h. In addition, manipulative experiments showed that anemones confronted with shelters that were obstructed with sediment had a 25% probability of fully retracting when Alpheus spp. were absent, compared to a 75% probability when shrimps had cleaned the shelter’s entry and internal passage. The analysis of field data indicated that the presence of alpheid shrimps as symbionts of B. annulata was 30% higher amongst anemones in close contact with sandy bottoms than when inhabiting crevices on the top or lateral walls of hard substrates, away from the sediment. Overall, our study concludes that den cleaning constitutes a quick and effective mechanism to assure the anemone’s full retraction into their den, and by keeping the sediment away, alpheids provide the necessary conditions that serve both the anemone’s and the shrimp’s higher chances of acquiring maximum protection from predators. This advantageous exchange in protection partially explains why alpheids are more frequently present in B. annulata in interface microhabitats where the benefit of the interaction is maximised.

Molecular data reshape our understanding of the life cycles of three digeneans (Monorchiidae and Gymnophallidae) infecting the bivalve, Donax variabilis: it's just a facultative host!

The coquina, Donax variabilis, is a known intermediate host of monorchiid and gymnophallid digeneans. Limited morphological criteria for the host and the digeneans’ larval stages have caused confusion in records. Herein, identities of coquinas from the United States (US) Atlantic coast were verified molecularly. We demonstrate that the current GenBank sequences for D. variabilis are erroneous, with the US sequence referring to D. fossor. Two cercariae and three metacercariae previously described in the Gulf of Mexico and one new cercaria were identified morphologically and molecularly, with only metacercariae occurring in both hosts. On the Southeast Atlantic coast, D. variabilis’ role is limited to being a facultative second intermediate host, and D. fossor, an older species, acts as both first and second intermediate hosts. Sequencing demonstrated 100% similarities between larval stages for each of the three digeneans. Sporocysts, single tail cercariae, and metacercariae in the incurrent siphon had sequences identical to those of monorchiid Lasiotocus trachinoti, for which we provide the complete life cycle. Adults are not known for the other two digeneans, and sequences from their larval stages were not identical to any in GenBank. Large sporocysts, cercariae (Cercaria choanura), and metacercariae in the coquinas’ foot were identified as Lasiotocus choanura (Hopkins, 1958) n. comb. Small sporocysts, furcocercous cercariae, and metacercariae in the mantle were identified as gymnophallid Parvatrema cf. donacis. We clarify records wherein authors recognized the three digenean species but confused their life stages, and probably the hosts, as D. variabilis is sympatric with cryptic D. texasianus in the Gulf of Mexico.

Early seral plant species’ interactions with an arbuscular mycorrhizal fungi community are highly variable

Arbuscular mycorrhizal fungi (AMF) are an important driver of plant community assembly, and as such may be critical for restoring plant communities. Previous work has shown that as plant communities develop, AMF density is a good predictor of what type of plant community is supported. However, interactions between plants, particularly facultative hosts, and AMF are often assumed from plant growth responses and lack concomitant AMF growth response data. We examined both plant and AMF responses in association using early- and mid-seral plant hosts and a homogenous AMF community. The goal was to determine how variable interactions are between facultative plant hosts and an AMF community. Plant responsiveness was measured using field soil with and without AMF. AMF density was measured by observing root colonization by AMF in a bioassay host plant grown in soils trained by the individual host plant species used in the plant responsiveness study. Plant species studied were highly variable in their interactions with AMF, and mutualisms, parasitisms, amensalisms and commensalisms were all prevalent. The presence of certain AMF facilitators may have a strong founder effect on plant communities and, where such feedbacks exist, identifying and utilizing these key interactions might facilitate the restoration of degraded ecosystems.

Some observations on trypanosoma pecorum (Bruce) and T. uniforme (Bruce)

The fact that antelope play a considerable part in nature as a reservoir for T. gambiense has now been thoroughly established. Both laboratory and field results agree in confirming the suspicion which for some time past has attached to these animals. In the case of T. gambiense , however, there is nothing very remarkable in the observation that the presence of the trypanosome in their blood apparently exerts no harmful effect on the antelope. T. gambiense cannot be considered as a fatal trypanosome for ruminants generally. In the case of pecorum, however, matters are different. This trypanosome, according to Bruce and his collaborators, causes a rapidly fatal disease in cattle and domestic animals generally. Though apparently widely distributed throughout Uganda, nothing definite is at present known concerning its true carrier in nature. The presence of the disease in districts where tsetse are unknown shows that some other agent is capable of conveying this trypanosome. The behaviour of laboratorybred Glossina palpalis as carriers is so uncertain that this fly would appear at most to be a facultative host, though doubtless under favourable circumstances it may play an important part in nature. Again, nothing is known concerning the existence of a natural reservoir for this trypanosome in Uganda, though Kleine has recently obtained species closely allied to, if not identical with, T. nanum and T. congolence from antelope in the neighbourhood of Tanganyika. The following experiments were undertaken with a view to discovering whether T. pecorum is pathogenic to antelope, and at the same time to test the power of these animals to act as a reservoir for the trypanosome:— A young bushbuck, born at the laboratory in January, 1911, was inoculated with blood of a monkey suffering from T. pecorum . After an incubation period of 15 days trypanosomes appeared in the blood of the bushbuck on May 31, 1911, being present for some days and then disappearing. Clean laboratory-bred G. palpalis were then fed upon the bushbuck and afterwards on clean monkeys. Those experiments are given in Table I. As will be seen, in only one instance was a positive transmission obtained, and this was unfortunately not entirely satisfactory, as will be explained below.