Behavioral variation according to feeding organ diversification in glossiphoniid leeches (Phylum: Annelida)

Adaptive radiation is a phenomenon in which various organs are diversified morphologically or functionally as animals adapt to environmental inputs. Leeches exhibit a variety of ingestion behaviors and morphologically diverse ingestion organs. In this study, we investigated the correlation between behavioral pattern and feeding organ structure of leech species. Among them, we found that Alboglossiphonia sp. swallows prey whole using its proboscis, whereas other leeches exhibit typical fluid-sucking behavior. To address whether the different feeding behaviors are intrinsic, we investigated the behavioral patterns and muscle arrangements in the earlier developmental stage of glossiphoniid leeches. Juvenile Glossiphoniidae including the Alboglossiphonia sp. exhibit the fluid ingestion behavior and have the proboscis with the compartmentalized muscle layers. This study provides the characteristics of leeches with specific ingestion behaviors, and a comparison of structural differences that serves as the first evidence of the proboscis diversification.

Leeches in the extreme: Morphological, physiological, and behavioral adaptations to inhospitable habitats

With more than 700 described species, leeches include morphological, physiological, and behavioral diversity and occur in terrestrial and aquatic habitats, including freshwater, estuarine, and marine ecosystems. Leeches inhabit a number of extreme environments, including extremes in temperature, moisture, salinity, pressure, light, and pollution. In some cases, leeches in extreme environments have specialized morphological, physiological, or behavioral adaptations to survive these conditions, yet unique adaptations are not apparent in some species. Leeches that inhabit inhospitable habitats occur in more than one branch or family of leech phylogeny suggesting that there have been independent invasions of environments with extreme conditions. Herein, we review examples of leeches that live in extreme conditions and the exceptional biology that has contributed to leeches being the most extreme annelids.

Developmentally regulated multisensory integration for prey localization in the medicinal leech

Medicinal leeches, like many aquatic animals, use water disturbances to localize their prey, so they need to be able to determine if a wave disturbance is created by prey or by another source. Many aquatic predators perform this separation by responding only to those wave frequencies representing their prey. As leeches' prey preference changes over the course of their development, we examined their responses at three different life stages. We found that juveniles more readily localize wave sources of lower frequencies (2 Hz) than their adult counterparts (8-12 Hz), and that adolescents exhibited elements of both juvenile and adult behavior, readily localizing sources of both frequencies. Leeches are known to be able to localize the source of waves through the use of either mechanical or visual information. We separately characterized their ability to localize various frequencies of stimuli using unimodal cues. Within a single modality, the frequency-response curves of adults and juveniles were virtually indistinguishable. However, the differences between the responses for each modality (visual and mechanosensory) were striking. The optimal visual stimulus had a much lower frequency (2 Hz) than the optimal mechanical stimulus (12 Hz). These frequencies matched, respectively, the juvenile and the adult preferred frequency for multimodally sensed waves. This suggests that, in the multimodal condition, adult behavior is driven more by mechanosensory information and juvenile behavior more by visual. Indeed, when stimuli of the two modalities were placed in conflict with one another, adult leeches, unlike juveniles, were attracted to the mechanical stimulus much more strongly than to the visual stimulus.

Cryptic radiation in erpobdellid leeches in xeric landscapes: a molecular analysis of population differentiation

Despite apparent long-term geographic isolation, many invertebrates demonstrate little apparent morphological differentiation. To examine underlying genetic differentiation, eight erpobdellid leech populations from widely dispersed northern Arizona aquatic ecosystems were examined by means of amplified fragment length polymorphism genetic markers. These populations were primarily Erpobdella punctata, though two populations, Motobdella montezuma and Motobdella sedonensis, have been described as novel taxa. Data from 137 polymorphic loci were used to estimate genetic heterogeneity (θ), migration rates (Nm), and genetic similarities (Dice's method) among these populations. Analysis of molecular variance and cluster analysis (unweighted pair-group method) were used to show population structure and to partition the genetic variance. Our analysis indicates that northern Arizona leech populations are genetically isolated (θ = 0.72, Nm = 0.09), with significant (p < 0.01) differentiation among populations. In addition, no relationship was found between genetic and geographic distances (r = 0.19, p = 0.22), which is consistent with long-term isolation even when populations are in close proximity. The large amount of genetic differentiation reveals levels of diversity and complexity not apparent from morphological comparisons alone and suggests that erpobdellid leeches in the arid landscape of the southwestern U.S.A. are in fact evolving independently from one another.

Phylogenetic relationships of three genera of Erpobdellidae (Hirudinoidea), with a description of a new genus, Motobdella, and species, Motobdella sedonensis

A new genus, Motobdella, is recognized for Erpobdella montezuma Davies, Singhal, and Blinn, 1985. In addition, a new species for this genus, Motobdella sedonensis, is described. Morphological characters that include the presence of crop caeca, number and size of the eyes, arrangement of the eyes, arrangement of ovisacs, position of the gonopore, structure and size of the sensilla, coloration, and position of the anus distinguish this new genus from Erpobdella and Nephelopsis. DNA fingerprinting methods were used to examine the phylogenetic relationships of these genera and corroborated the morphological data supporting the evolution of this genus with two distinct species.

The evolutionary importance of mechanoreception in three erpobdellid leech species

The ability of an erpobdellid leech, Erpobdella montezuma, to discriminate between two congeneric amphipod prey (Hyalella montezuma and Hyalella azteca) through mechanoreception was examined. Both E. montezuma and H. montezuma, a pelagic filter feeder, are endemic to the near thermally constant environment of Montezuma Well, Arizona, and form a highly specialized predator-prey relationship. In contrast, H. azteca, a benthic detritivore, is widely distributed throughout North America. Erpobdella montezuma was highly responsive to the prey signals of the endemic H. montezuma and showed only a limited response to H. azteca. An inverse relationship occurred between the frequency of attack and size of the leech. The abilities of Erpobdella punctata and Nephelopsis obscura, neither found in Montezuma Well, to detect the signals of both amphipod prey were also examined. These species with non-specialized diets showed a low response to the signals of both prey species. This study demonstrates that very close predator-prey relationships can develop over evolutionary time in isolated aquatic systems through the use of mechanoreception.

Morphology of chemosensory organs required for feeding in the leech Hirudo medicinalis

Sensilla that line the upper edge of the lip in the leech Hirudo medicinalis and that contain chemoreceptors required for feeding were examined in the scanning and transmission electron microscopes. The sensilla include two size-classes of ciliated button-like mounds--one about 35 microns in diameter and another about 10 microns in diameter. The larger sensilla are at the center of unpigmented patches of skin which are visible in the light microscope, while the smaller sensilla have not been previously described as distinct structures. Electron microscopy, though not light microscopy, shows that the lip sensilla differ markedly from the segmental sensilla of the leech, which have been shown to mediate mechanoreception and photoreception. In particular, the chemosensory lip sensilla contain multiciliated cells with cilia of a uniform length, whereas the segmental sensilla contain uniciliated cells with long, whip-like cilia, as well as multiciliated cells with short, stiff cilia. Thus, the two types of sensilla differ morphologically as well as functionally. In addition to the ciliated sensilla along the upper lip, structures consisting of a short, club-like process surrounded by granular material were observed inside the mouth. These structures may also be chemosensory organs.