Die Feinstruktur der Kolbenzellen (Schreckstoffzellen) in der Epidermis von Astyanax mexicanus Filippi 1853 (Characinidae,Pisces) und seinen Höhlenderivaten “Anoptichthys”

Fine Structure of the Club Cells (Alarm Substance Cells) in the Epidermis of Astyanax mexicanus Filippi 1853 (Characinidae, Pisces) and its Cave Forms “Anoptichthys” The club cells in the epidermis of Astyanax mexicanus are of the same ultrastructure as those in other Ostariophysan fish. There are also no essential differences to be found between the club cells of epigean Astyanax mexicanus and its cave forms “Anoptichthys”. Our findings correspond to former statements in that the function of the club cells producing and releasing alarm substances has been maintained in the cave forms.     

Behavior in an ‘intermediate’ population of the subterranean-dwelling characid Astyanax fasciatus

Synopsis A population of the characid Astyanax fasciatus was found living at the outflow of a subterranean source of water. Field observations revealed differences in behavior when compared with river populations. Affinity of this fish for the subterranean cavity was evidenced by behavior and distribution of individuals. Fish almost always carried bait into the subterranean cavity prior to feeding and also went into the cavity at night. Three factors may influence the affinity for the subterranean source of water: 1) protection against aerial predation, 2) the advantage to fishes of hovering in shade, 3) sheltering for reproduction. These observations suggest that cave colonization may take place actively rather than accidentaly, that behavioral changes may preceed morphological ones during initial stages of cave entry, and that behavioral adaptations may occur quite rapidly.     

Breeding biology and longevity of Russet-crowned Motmots in central Mexico

ABSTRACT.   Motmots, with their distinctive racketed-tails, represent one of the most easily recognized tropical birds, yet little is known about the basic natural history of most species in the family Momotidae. We report basic breeding biology and longevity of Russet-crowned Motmots ( Momotus mexicanus ), a medium-sized Neotropical bird that ranges from northwest Mexico to central Guatemala. We monitored nest success of eight pairs from 1 May to 17 July 1998 in tropical deciduous forests in central Mexico. Motmots laid an average of 4.1 eggs and incubated for approximately 20 d. Four of eight nests fledged young. Of these four nests, average hatching success was 69% and average fledgling success was 56%. The mean duration of the nestling period at three nests was 33.7 d. Based on the recapture of one individual bird in April 2008, we provide a longevity estimate that Russet-crowned Motmots can survive at least 11 yr in the wild. These data on nesting success and longevity add to our limited knowledge of the natural history of this understudied species.     

SHOREBIRD HABITAT USE AND NEST-SITE SELECTION IN THE PLAYA LAKES REGION

Abstract: Wetlands in the Playa Lakes Region (PLR) provide important habitats for wintering waterfowl, cranes, and both migrant and breeding shorebirds. Playa Lakes Region wetlands experience naturally fluctuating hydroperiods but are exposed to anthropogenic stresses, which are exacerbated during summer and may influence PLR wetland occupancy and selection by breeding shorebirds. We examined wetland-scale habitat use and nest-site selection of the 4 dominant shorebirds (American avocets [Recurvirostra americana], black-necked stilts [Himantopus mexicanus], killdeer [Charadrius vociferus], snowy plovers [C. alexandrinus]) nesting in playas, saline lakes, and in both created and riparian wetlands in the PLR of Texas, USA. All 4 species nested in saline lakes. Only avocets and killdeer nested in playas, and snowy plovers nested in riparian wetlands. No nests were found in created wetlands. Wetland habitat changed (P < 0.001) during the breeding season, while water habitats generally decreased. Used (i.e., shorebirds found nesting) wetlands had more (P < 0.05) mudflats than non-used (i.e., shorebirds not found nesting) wetlands, which had more (P < 0.05) dry habitats. Used and non-used wetlands had similar (P > 0.05) amounts of water habitats. Nests were located close to vegetation on bare dry ground and dry ground with vegetation. Because water is ephemeral in PLR wetlands, shorebirds must select—in a somewhat predictive manner upon arrival—wetlands with suitable nest-site and brood-rearing habitat. Although surface water is necessary for nesting, its presence is not adequate for delineating suitable PLR wetland habitat for breeding shorebirds. Our findings that created wetlands cannot compensate for regional wetland losses in habitat or function highlights the need for conservation of natural PLR wetlands     

The range expansion of the great-tailed grackle (Quiscalus mexicanus Gmelin) in North America since 1880

Aims This study aimed to document and describe the current range expansion of the great‐tailed grackle (Quiscalus mexicanus Gmelin) into the USA. By examining the habitat associations and pattern of spread of this species, I intended to determine the factors responsible for this remarkable expansion by a tropical species into a temperate environment. Location This study focused on the spread of the great‐tailed grackle in the continental USA, Canada and Baja California. Methods I used published records, museum specimens, and egg collections to document this range expansion from 1880 through 2002. In addition I surveyed large portions of Arizona, Nevada, southern Utah and southern California for great‐tailed grackles during 2000 and 2001. The data gathered was used to create maps in order to quantify the rate of spread of this species. Results Between 1880 and 2000 the great‐tailed grackle expanded its breeding range in the USA from c. 64,000 km² to more than 3,561,000 km², an increase of 5530%. The average annual rate of increase is 3.4%, but has lessened during the past 20 years. Northward movement in the eastern portion of the range has slowed down, reflecting this decrease. However, in the central and western portion of the species range, the rate of northward movement is still accelerating. During this expansion, the average time between first sighting in a state and first breeding was 5.8 years. The species has become less migratory during its range expansion, wintering in 17 of the 20 states where it breeds. Main conclusions This range expansion has been marked by great‐tailed grackles preferring human‐modified environments as breeding grounds, especially in the western states. This association appears to benefit the species in two ways; nest predation is lessened in such areas compared with natural conditions, whereas human activities tend to generate an abundant and consistent food supply for feeding offspring. Wintering birds are often associated with cattle feed lots and large‐scale dairies, where abundant waste grain provides them with a reliable food supply. Given the continued human population increase throughout large areas of the western USA, the great‐tailed grackle will continue its range expansion.     

Common garden experiment reveals pathogen isolate but no host genetic diversity effect on the dynamics of an emerging wildlife disease

Host genetic diversity can mediate pathogen resistance within and among populations. Here we test whether the lower prevalence of Mycoplasmal conjunctivitis in native North American house finch populations results from greater resistance to the causative agent, Mycoplasma gallisepticum (MG), than introduced, recently‐bottlenecked populations that lack genetic diversity. In a common garden experiment, we challenged wild‐caught western (native) and eastern (introduced) North American finches with a representative eastern or western MG isolate. Although introduced finches in our study had lower neutral genetic diversity than native finches, we found no support for a population‐level genetic diversity effect on host resistance. Instead we detected strong support for isolate differences: the MG isolate circulating in western house finch populations produced lower virulence, but higher pathogen loads, in both native and introduced hosts. Our results indicate that contemporary differences in host genetic diversity likely do not explain the lower conjunctivitis prevalence in native house finches, but isolate‐level differences in virulence may play an important role.     

Intraspecific variation in Diplophallus polymorphus (Rudolphi, 1819) (Cestoda: Acoleidae) from avocets and stilts (Recurvirostridae) in North America

Diplopallus polymorphus (Rudolphi, 1819) (Cestoda: Acoleidae), hitherto recorded from avocets Recurvirostra avosetta L. and stilts Himantopus himantopus (L.) (Recurvirostridae) in Europe, Asia and Africa, is reported for the first time as a parasite of Recurvirostra americana Gmelin, 1788 and Himantopus mexicanus (Milller, 1776) in the Pacific, Central and Mississippi migratory flyways of North America. D. polymorphus is redescribed, as it shows great intraspecific variation in the number (20–25) and size (0.087-0.122 mm) of the rostellar hooks and in the position of the cirrus-sac and relation of the external seminal vesicle to the longitudinal excretory vessels. It is found that the intraspecific variations are neither related to host nor to locality of the host. The possible synonymy of D. polymorphus with D. colli Ahern & Schmidt, 1976 and with Himantocestus blanksoni Ukoli, 1965 is discussed.     

MALE MATE CHOICE AND THE EVOLUTION OF FEMALE PLUMAGE COLORATION IN THE HOUSE FINCH

The house finch (Carpodacus mexicanus) is a sexually dichromatic passerine in which males display colorful plumage and females are generally drab brown. Some females, however, have a subdued version of the same pattern of ornamental coloration seen in males. In previous research, I found that female house finches use male coloration as an important criterion when choosing mates and that the plumage brightness of males is a reliable indicator of male nest attentiveness. Male house finches invest substantially in the care of young and, like females, stand to gain by choosing high-quality mates. I therefore hypothesized that a female's plumage brightness might be correlated with her quality and be the basis for male mate choice. In laboratory mate choice experiments, male house finches showed a significant preference for the most brightly plumaged females presented. Observations of a wild population of house finches, however, suggest that female age is the primary criterion in male choice and that female plumage coloration is a secondary criterion. In addition, yearling females tended to have more brightly colored plumage than older females, and there was no relationship between female plumage coloration and overwinter survival, reproductive success, or condition. These observations fail to support the idea that female plumage coloration is an indicator of individual quality. Male mate choice for brightly plumaged females may have evolved as a correlated response to selection on females to choose brightly colored males.