Alistair McVean

Intraspecific variation in the Egyptian scorpion Scorpio maurus palmatus venom collected from different biotopes

The present study was conducted to explore the following hypotheses: (i) do scorpions (Scorpio maurus palmatus) from different biotopes exhibit intraspecific diversity in their venom? (ii) if so, is this variation associated with ecological or genetic factors, geographical distance, and/or multiple interrelated parameters? To address these questions, scorpions were collected from four geographically isolated localities in Egypt. Three of these locations are from mutually isolated pockets in the arid biotope of Southern Sinai (Wadi Sahab, El-Agramia and Rahaba plains). The fourth population was sampled from the semiarid biotope of Western Mediterranean Costal Desert (WMCD). Using reducing gel electrophoresis (SDS-PAGE), we have shown biotope-specific variation in the expression of peptides from scorpions collected from these distinct areas. WMCD sourced venom samples contain higher molecular weight protein components (219, 200, 170, 139, 116 kDa) than Southern Sinai scorpion venom samples. The Southern Sinai venom is characterized by the presence of 11 protein bands (93-0.58 kDa) that are not mirrored in the individual venom samples of WMCD. Bands of 33 and 3.4 kDa were characteristics of all individual venom samples of the scorpion populations. Even within Southern Sinai area, Sahab venom contains five fractions that are not detected in both El-Agramia and Rahaba venom samples. Moreover, male and female venom analysis revealed some sex-related proteomic similarities and differences between scorpion populations. Female venom appears to be more complicated than the male venom. Female venom samples showed bands of 219, 200, 77.5, 55.5, 45, 39, 37, 24 and 16 kDa which were absent in the male venom. The random amplified polymorphic DNA (RAPD) technique was used to estimate the genetic distance between the four scorpion populations. The RAPD data confirmed the genetic diversity at molecular level among the sampled populations. More than 77 RAPD bands (ranging in size from 125 to 15,000 bp) were defined from the four scorpion populations. Of the 77 bands, 57 (76.2%) were polymorphic and 20 were monomorphic among the populations. The similarity coefficient data of venom and DNA were used to construct separate dendrograms, which grouped together the Southern Sinai populations and these were some distance away from the WMCD population. Taken together, we suspect that a combination of local environmental conditions, geographical separation and genetic separation may play a major role in the intraspecific variation of venom of S. m. palmatus.

The incidence of autotomy in Carcinus maenas (L.)

Abstract A total of 1023 individuals of the common shore crab, Carcinus maenas (L.), were obtained from the environs of Whitby Harbour and Robin Hoods Bay. The bulk of the sample was taken from the sublittoral zone, but crabs from a sheltered shore were included. Each crab was measured, sexed and examined for the incidence of autotomized and regenerated limbs. There was a positive correlation between the incidence of autotomy and carapace width for crabs in both the sublittoral zone and the exposed intertidal zone. In sublittoral crabs the males suffered a higher incidence of autotomy than did the females and the incidence of cheliped autotomy was higher than for the walking limbs. The discrepancy between the loss of the chelipeds and walking limbs was reflected in a similar disparity between the occurrence of the regenerated chelipeds and walking limbs. Crabs on an exposed shore suffered a higher incidence of autotomy than did those from a sheltered shore. There were more crabs with cumulative limb losses than would be expected which suggests that once a crab enters into a state of autotomy it becomes increasingly vulnerable to the loss of another limb. Only 1 % of the population of sublittoral crabs would be expected to carry the loss of five limbs at once. No crabs were found with six or more limbs missing.

The effects of lowered temperature on spontaneous eye movements in a Teleost fish

A new opto-electronic method has been used to measure spontaneous eye movements in a lightly restrained unanaesthetized marine teleost fish (Parore). The normal scanning pattern of eye movement is similar to that previously described in goldfish. The effects of cooling on eye movements were investigated by 2 degrees C step changes down from ambient temperature (13-14 degrees C). Lowered temperature altered the scanning pattern, decreased saccade velocity, increased mean saccade amplitude and impaired the ability of the fish to hold the eye stationary between saccades. All eye movements stopped at temperatures around 6 degrees C, but could be restored by subsequent warming.

Brain function in antarctic fish: Activity of central vestibular neurons in relation to head rotation and eye movement

SummaryRecordings were made from central vestibular neurons responding to horizontal head rotation in antarctic fish,Pagothenia borchgrevinki, at a temperature close to 0 °C. The spontaneous activity of these units varied between 0 and 56 Imp/s with a mean value of 20. Almost all units responded to horizontal rotation with a maximum firing rate that was approximately in phase with head velocity, either towards the recording side (type I units) or away from the recording side (type II), with no alteration of firing pattern during saccadic eye movements. The mean gain of these units was 2.6 Imp/s/ℴ/s at 0.35 Hz which is higher than that reported for central vestibular neurons in other fish.

Neuromodulatory effects of acetylcholine and serotonin on the sensitivity of leech mechanoreceptors

1. Each segmental ganglion of the leech Hirudo medicinalis contains 6 touch (T) cells, 4 pressure (P) cells and 4 nociceptive (N) cells. The receptive terminals of these cells innervate the skin in discrete areas. These cells are known to have extrasynaptic receptors. 2. We tested the effect of transmitter substances present in leech CNS on the sensitivity of T and P cells to mechanical stimuli. Substances tested included octopamine, FMRFamide, proctolin, substance P, glutamate, GABA, acetylcholine and serotonin. 3. Only acetylcholine and serotonin had consistent effects. Serotonin (1 x 10(-3) M) increased the number of action potentials of T cells elicited by a standard stimulus. Serotonin (1 x 10(-4) M) and acetylcholine (1 x 10(-3) M) increased the number and frequency of action potentials in P cells.

TOXIN EVOLUTION IN SCORPION VENOM: EVIDENCE FOR TOXIN DIVERGENCE UNDER STRONG NEGATIVE SELECTION IN LEIURUS QUINQUESTRIATUS SUBSPECIES

The Buthid scorpion Leiurus quinquestriatus is divided into two sub-species whose region of contact occurs at the Suez Isthmus. L.q. quinquestriatus, found in the North Africa is distinguished from L.q. hebraeus by minor differences in morphology. Despite the very high similarity in body plan, out of the 24 toxins isolated from this species none is common to both sub-species, suggesting a degree of molecular divergence not apparent at the morphological level. We show, by comparison with two sets of reference proteins from humans and Old-World monkeys, that divergence of toxins with common structures and functions in these two sub-species has occurred under conditions of strong negative selection. Potential selection pressures responsible for toxin divergence are discussed, including the role of conflicting interests during courtship.

Autotomy inCarcinus maenas: The role of the basi-ischiopodite posterior levator muscles

Summary1.The anatomy of the muscles attaching to the dorsal rim of the basi-ischiopodite and the associated cuticular structures ofCarcinus maenas, Maia squinado andPagurus bernhardus was examined.2.There are four such muscles in brachyuran walking limbs (Figs. 1A and 5B) each of which has a specific function as outlined in Table 1. There is a further subdivision of muscle function in the cheliped (Fig. 1B).3.Myograms obtained from the posterior levator muscles (PPLM and RPLM) of the walking limbs reveal that in brachyura the muscles are physiologically distinguishable both during limb levation and autotomy (Fig. 2).4.The antagonistic action of these muscles upon autotomy enables the anterior levator muscle force to be rapidly switched from a cuticular projection onto the cuticular plug which forms the link across the limb breakage plane (Figs. 4 and 7).5.The reflex control of autotomy by the cuticular stress detector (CSD1) was analyzed.

Temperature compensation in myotomal muscle: antarctic versus temperate fish

SynopsisContraction time of an isolated white muscle from the temperate water Girella tricuspidata is proportional to temperature and inversely proportional to fish size. Between ambient (14°C) and 8° C muscle from all sizes of fish is similary affected by temperature; the lower the temperature the more the contraction time is slowed. Below 8° C muscle from large fish is affected more than is muscle from small fish. Contraction time of white muscle in the antarctic notothenioid Pagothenia borchgrevinki is about twice as fast as that of Girella tricuspidata at temperatures between 2–12°C, but at normal body temperature, contraction time of muscle from Girella tricuspidata (14°C) is about twice as fast as that of Pagothenia borchgrevinki (−1.9°C).

A comparison of the performance of two sensory systems in host detection and location in the medicinal leech Hirudo medicinalis

1. Mechanical and visual stimuli associated with surface waves were separated into their two components. 2. Unfed leeches responded to the mechanical component of artificially generated surface waves by swimming towards their source. 3. Leeches also responded to and orientated towards the source of the waves using visual cues derived from the same surface waves. 4. Visual stimuli elicited fewer and less accurate responses.

Postembryonic Growth of Two Peripheral Sensory Systems in the Medicinal Leech Hirudo medicinalis

The midbody segments of Hirudo medicinalis have two types of sensory cilia that project from the skin into the surrounding water. These are the proposed mechanosensory S cilia and the putative chemosensory G cilia. The cells bearing these cilia are clustered together into structures known as sensilla. The skin of each midbody segment is externally divided into five annuli. Fourteen large sensilla carrying S and G cilia are found on the central annulus of each segment. Small sensilla carrying only G cilia are found on all five annuli. In this paper we show a positive correlation between the size of a neural sensillum and the number of S and G cilia it contains. Any one leech contains a range of sizes of neural sensilla, but the average area increases with the weight of the leech. In contrast, the annular sensilla show only a modest increase in size with leech weight.