<p> Skunk spray produced in the anal glands of the striped skunk can have extremely adverse effects on potential predators, who then learn to avoid provoking these animals in the future. Despite this spray being an extremely effective predator deterrent, few studies have assessed the molecular constituents found within striped skunk spray, and no studies have attempted to assess how important ecological factors could influence the strength of the spray. The goal of this study was to assess the honesty of striped skunk pelage and the influence of predation risk and life history on skunk musk by measuring the variation in the amounts of the major noxious chemicals of skunk spray, using gas chromatography-mass spectrometry (GC-MS). A total of fifty-eight anal secretion samples and dorsal stripe images were collected from striped skunks from two separate locations differing in mammalian and avian predation risk. Overall, the findings of this study support the hypothesis that striped skunk spray and pelage whiteness varies more in areas with greater risk of predation by mammals, and anal secretion noxiousness is influenced by the skunk&rsquo;s weight, sex, and reproductive state. The aposematic coloration exhibited by skunks as well as the defensive spray mechanism is largely influenced and selectively maintained by mammalian predation pressures.</p><p>

The objective of this study was to taxonomically revise the 41 nominal species found within the Brachirus species complex (Order Pleuronectiformes; Family Soleidae). This complex is recognizable by a combination of characters: the structure of the supracranial portion of the dorsal fin which lack pterigiophores with their proximal ends directly over the cranium, by the joined dorsal, anal and caudal fins, and by the anterior tip of the dorsal fin almost reaching the upper jaw. This revision is based on the morphological and meristic examination of 34 type and 717 non-type specimens for all available nominal species. The type material was examined for twenty species. The remaining species were assessed from the original type description. It was found that the Brachirus species complex is made up of four genera including 19 valid species: Brachirus (14), Achiroides (1), Dexillus (3), and Paradicula (1). Eight of the nominal species do not belong to the Brachirus species complex and have been removed from the scope of this study. Achiroides, characterized by the rudimentary pectoral fins, contains a single valid species, A. melanorhynchus (Bleeker 1851) and three synonyms (Synaptura aenea Smith 1931, Anisochirus harmandi Sauvage 1878, and Plagusia leucorhynchos Bleeker 1851). Dexillus , characterized by the close proximity of the eyes, contains three valid species: D. macrolepis (Bleeker 1858), D. megalepidoura (Fowler 1934), and D. muelleri (Steindachner 1879). D. muelleri is a senior synonym of the nominal species Synaptura arafurensis Gunther 1880. Paradicula, unique in having the gill openings restricted to the base of the pectoral fins, contains a single valid species, P. setifer Paradice & Whitley 1927. The remaining Brachirus species cannot yet be defined as being monophyletic. Brachirus contains 14 valid species: B. aspilos (Bleeker 1852) (synonyms: Synaptura heterolepis Bleeker 1856, S. marmorata Bleeker 1853, and S. sorsongonensis Evermann & Seale 1907), B. sundaicus (synonyms: Bleeker 1870--75) (Synaptura cinerea De Vis 1883 and S. nigra MacLeay,1880), B. selheimi (Macleay 1882) (synonyms: B. salinarum Ogilby 1910, and Synaptura villosus Weber 1907), B. foliacea (Gunther 1862) (synonym: Synaptura filamentosa Sauvage 1878), B. siamensis (Sauvage 1878) (synonyms: Synaptura krempfi Durand 1940 and Chabanaudetta smithi Joglekar 1971), B. breviceps Ogilby 1910, B. cinerascens (Gunther 1862), B. fitzroiensis (De Vis 1882), B. orientalis (Bloch & Schneider 1801), B. pan (Hamilton 1822), B. panoides (Bleeker 1851), B. dicholepis Peters 1877, B. swinhonis Steindachner 1867, and B. canus Gray 1854. An identification key of valid species belonging to the Brachirus species complex is provided.

This dissertation examines the early phylogenetic divergences of the phylum Platyhelminthes using molecular sequence data, with an emphasis on the placement and evolutionary significance of several enigmatic and largely overlooked lineages. Firstly, I assess platyhelminth interrelationships using a representational sampling of all free-living orders for the “standard” 18S and 28S rRNA loci (plus two mtDNA markers). These analyses place numerous problematic taxa, most notably Gnosonesimida, which is recovered in a position consistent with the classical hypothesis in which this order retains a primitive form of ectolecithality. I also investigate the status of the crustacean-parasitic genus Genostoma, classified presently within Fecampiida, which has however been proposed on the basis of ultrastructural data to lie outside this order. These efforts robustly position Genostoma as the sister-taxon to the free-living order Prolecithophora, suggesting the recognition of a new higher taxon to accommodate this morphologically distinct, but poorly diverse lineage. To overcome the inherent limits of rRNA phylogenetics, I used massively parallel sequencing to survey transcriptomes from representatives of all “turbellarian” orders. From concatenation and consensus analyses of 512 orthologs, a robust signal of platyhelminth phylogeny emerges, congruent with previous results but also presenting several unanticipated relationships. Most notable among these, the monospecific order Bothrioplanida is recovered as the sister-group of Neodermata, the major vertebrate-parasitic clade within Platyhelminthes. These analyses prompt consideration of novel hypotheses on the origins and consequences of parasitism within Platyhelminthes, and motivate many previously unexplored comparisons among free-living taxa. The position of Platyhelminthes within Spiralia, and the related question of whether the phylum is “primitive” in morphology, remains controversial. I therefore also used transcriptomic data to resolve the phylogeny of Spiralia, with emphasis on the status of the “platyzoan” phyla, and on positioning several problematic interstitial lineages. These data robustly position Lobatocerebrum and Diurodrilus as members of Annelida. I also recover strong support for the non-monophyly of the platyzoan phyla, with Gnathifera as the earliest-splitting branch and a clade of Platyhelminthes and Gastrotricha as the nearest relative of Trochozoa. This phylogeny hence simultaneously highlights the importance of “reductive” processes in the evolution of interstitial organisms, as well as the possibility of the primitive nature of at least some of the “simple” features that have classically inspired zoological interest in Platyhelminthes. Finally, I present a focused inquiry on the internal phylogeny of one “isolated” flatworm clade, the continental order Prorhynchida. The recovered topology is broadly congruent with traditional classification, with most prorhynchid species falling into two genera. Remarkably, however, two rare taxa that share morphologically similar copulatory apparatus are recovered as unrelated basal branches, indicating the probable plesiomorphic nature of this morphology. Also, a little-known groundwater species, Geocentrophora boui, is supported as the sister taxon of the self-fertilizing genus Xenoprorhynchus, illuminating the functional specialization of the “copulatory” apparatus as a venom delivery system in this lineage. Field collections from this study uncovered over 31 new species, many of these unexpectedly terrestrial, more than doubling the known diversity of the order, and highlighting the need for continued systematic research on these remarkable but understudied animals.

No description available.

The homeo box is a 180 base pair DNA sequence that is found in some genes of Drosophila which are crucial to its embryogenesis. Hence, this sequence has been used extensively as a probe to search for genes which may play a role in the development of vertebrates. Sequences with homology to Drosophila homeo boxes have been found in a number of vertebrate species including mouse, man and frog. The purpose of this thesis was to clone homeo box sequences from the Mexican axolotl, an animal which has had a distinguished history in the study of development. Clones cross-hybridizing with the Drosophila Antennapedia homeo box were obtained from a partial genomic library enriched for such sequences. One clone (pAhox1) contained a homeo box sequence (Ahox1) which is 66% homologous to the Antp sequence, and is most closely related to the mouse Hox-1.6 homeo box (84% identity). Total RNA from several embryonic stages was probed with a 560 bp KpnI fragment of pAhox1 containing the homeo box (HB-Kpn). This showed that transcripts hybridizing to this sequence were detected only in neurula, and tail bud axolotl embryos, suggesting that this sequence is developmentally regulated. Tissue specific expression of Ahox1 was examined in dissected neurula and tail bud embryos. In the neurula, transcripts hybridizing to Ahox1 were found to be restricted to the posterior two thirds of the neural plate and in tail bud embryos from the anterior margin of the gill bulge to the pronephric duct. Another clone (pAhox2) obtained from this library contained a partial homeo box sequence, and its homology to the Antp sequence was found to reside in the last 60 nucleotides of the homeo box, a region thought to be responsible for DNA binding. One powerful method to study gene function in vertebrates has been the introduction of cloned DNA sequences into developing organisms by microinjection. Expression of exogenous sequences in fertilized axolotl eggs were therefore examined, by using constructs consisting of a eukaryotic promoter, fused with the E. coli lacZ coding sequence which could be detected by histochemical staining. Expression from several eukaryotic promoters was observed, and the strongest expression observed was with the mouse hsp68 promoter. In order to examine the possible role of Ahox1, a construct was prepared with HB-Kpn fused to the mouse hsp68 promoter. When this construct was microinjected into fertilized axolotl eggs, defects in the anterior neural tissues were observed. These were first observed in the neurula stage of development, when Ahox1 expression is first observed. The abnormalities observed in these embryos were in neural tissues not normally expressing Ahox1.

The locations and migration of the embryonic primordia which form the heart are well known. However, the processes whereby the heart-forming mesoderm is induced, and the later mechanisms controlling the differentiation and morphogenesis of the heart are only poorly understood for any system. An important model system for studying heart induction and differentiation is the cardiac-lethal (c) mutant in the axolotl (Ambystoma mexicanum). Embryos homozygous for the c gene develop hearts which never begin to beat, become severely deformed due to the lack of circulation, and die shortly after hatching. The mutation was believed to affect the tissue responsible for heart induction, the anterior (pharyngeal) endoderm, rendering it incapable of supplying the appropriate inductive stimuli. The inductive failure hypothesis is largely based on an assumption. The assumption is that the timing of heart induction is the same in the axolotl as has been reported for another urodele species (Taricha torosa). As well, this hypothesis is based on the finding that wild-type heart mesoderm does not form beating hearts when transplanted into c/c embryos at late tailbud stages 28-29. On the basis of this evidence, it has been suggested that wild-type heart mesoderm does not receive the proper inductive signals in the mutant environment. However, it has also been suggested that the induction occurs much earlier in another species of Ambystoma than in T. torosa; the timing of the inductive process in the axolotl has never been determined. The presence of a specific activator and inhibitor of heart differentiation, both produced by the heart mesoderm itself, provides evidence that the later phases of heart formation (i.e. the organization of contractile proteins into functional sarcomeres, and possibly the early morphogenesis of the heart tube) are probably under the control of a two-morphogen reaction-diffusion system. Such systems have been demonstrated to control pattern formation in one invertebrate organism, and have been proposed to control morphogenesis in a variety of other systems. However, this study is the first direct, experimental evidence for a reaction-diffusion mechanism controlling the development of any vertebrate organ system. (Abstract shortened by UMI.)

This study provides baseline data on the River Redhorse (Moxostoma carinatum; Moxostomatini: Catostomidae) in Canada. Sampling focussed on the Mississippi and Gatineau Rivers, in the National Capital Region, in 1998 and 1999. Spawning occurred in rocky, shallow (&lt;2m) fast-water sections in May and June when the temperature reached 17&deg;C. In the Mississippi River, post-spawn specimens were captured on a variety of substrates in deeper waters. Both opercular bones and scales (n = 19) recorded accurate age until age XII after which only the opercular bone provided clear annuli. Growth for both sexes was defined by the following equation: total length at age (mm) = 0.0905 (age)3 - 5.1452 (age)2 + 95.94 (age) + 0.367. Population sizes were assessed through capture-recapture methods. The population size in the Mississippi River was estimated at 622 (+/-6.3 s.d.). The spawning population of the Gatineau River was estimated at 1216 (+/-915 s.d.). It is suggested that the species remains a species of "special concern" in Canada.

This thesis examines the branchial mechanisms utilized by freshwater fish to regulate internal acid-base status and presents a model to explain the underlying basis of the compensatory processes. Rainbow trout, Oncorhynchus mykiss, brown bullhead, Ictalurus nebulosus, and American eels, Anguilla rostrata, were examined under a variety of experimental treatments which induced both respiratory (hyperoxia, hypercapnia) and metabolic (post-hyperoxia, post-hypercapnia, HCl infusion, NaHCO$\sb3$ infusion) acid-base disturbances. Acid-base-regulation was achieved by appropriate adjustments of Na$\sp+$ and Cl$\sp-$ net fluxes across the gills which, in turn, were accomplished by variable contributions of three different branchial mechanisms; (i) morphological adjustments to the gill epithelium, (ii) changes in internal (H$\sp+,$ HCO$\sb3\sp-)$ and external (Na$\sp+,$ HCO$\sb3\sp-)$ substrate availability, and (iii) differential changes in Na$\sp+$ versus Cl$\sp-$ net fluxes through regulation of Cl$\sp-$ efflux. This thesis determined the variable contribution of each of these mechanisms to overall compensation of acid-base disturbances. In brown bullhead and trout, respiratory acidosis caused a reduction in chloride cell (CC) surface area whereas alkalosis was associated with increases in CC surface area. Increases in the density of microvilli displayed on the external surface of the PVC coupled with ultrastructural modifications during hypercapnic acidosis were associated with increases in Na$\sp+$ uptake $\rm(J\sb{in}\sp{Na+}).$ In addition to the effect that alterations in CC surface area have on the rate of Cl$\sp-$/HCO$\sb3\sp-$ exchange $\rm(J\sb{in}\sp{Cl-}),$ it was demonstrated that changes in the concentration of the internal counter-ion (HCO$\sb3\sp-)$ may alter the rates of acid-base compensation. When (HCO$\sb3\sp-$) is elevated, $\rm J\sb{max}\sp{Cl-}$ is elevated thereby increasing the capacity to excrete HCO$\sb3\sp-$ via the Cl$\sp-$/HCO$\sb3\sp-$ exchanger over and above those determined by CC morphology. This is an important mechanism to increase the rate of acid-base compensation during metabolic alkalosis. (Abstract shortened by UMI.)

The family Samaridae has 28 nominal species or subspecies, 22 of which are recognized in this study. Four new species (Samariscus sp., Samaris sp., Samaris sp. 1 and S. sp. 2) are described, two species names resurrected (S. cacatuae and S. onatus) and two species (S. filipectoralis and S. sunieri) and one subspecies (Samaris cristatus erythraeus) are synonymized. An artificial key was constructed for all species. The family is shown to be monophyletic, as are the three genera comprising the family; Plagiopsetta being the most plesiomorphic. Samaris and Samariscus are sister groups. Numerous apomorphies corroborate the monophyly of the S. cristatus complex (Samaris cristatus, S. cacatuae, S. ornatus and S. sp). In Samariscus, S. nielseni, S. corallinus and S. triocellatus form a monophyletic group. The family is restricted to the Indo-West Pacific. Species numbers are highest in the Indo-Malaysian region, drop off with increasing distance and are not found in the extreme eastern Pacific due to the eastern Pacific barrier.

To reduce predation on their progeny, passerines evolved two basic nesting patterns: (1) concealing nests or constructing them in inaccessible places, or (2) breeding inside cavities where offspring are relatively protected. These two nesting patterns seem to lead to different length of nesting cycle. Nice (1957) was the first to report that cavity-nesting species have a longer nestling period than open-nesting species. Why does such a difference in nestling period exist? The goals of my study were: (1) to verify the earlier observation that cavity nesters have a longer nestling period than open nesters; (2) to test the assumption that predation is more intense on nest contents of open nesters than cavity nesters, thereby presenting an important selective force favoring different lengths of the nestling periods of the two groups; and (3) to test two hypotheses on the occurrence of different length of nestling periods between the two groups of passerines. (Abstract shortened by UMI.)