Chromosome banding and DNA replication patterns in bird karyotypes

The karyotypes of the domestic chicken (Gallus domesticus), Japanese quail (Coturnix coturnix), and griffon vulture (Gyps fulvus) were studied with a variety of banding techniques. The DNA replication patterns of bird chromosomes, analyzed by incorporation of 5-bromodeoxyuridine (BrdU) and deoxythymidine (dT), are presented here for the first time. In particular, the time sequence of replication of the ZZ/ZW sex chromosomes throughout the S-phase was meticulously analyzed. BrdU and dT incorporation are very useful methods to identify homoeologies between karyotypes, as well as rearrangements that occurred in the macroautosomes during speciation. The Z chromosomes of the three birds displayed the same replication patterns, indicating a high degree of evolutionary conservation. In the homogametic male, BrdU and dT incorporation revealed no evidence of asynchronous replication between euchromatic bands in the ZZ pair. The same was true of the three Z chromosomes in a triploid-diploid chimeric chicken embryo. Minor replication asynchronies between the homologous ZZ or ZZZ chromosomes were restricted to heterochromatic C-bands. These results confirm that, in the ZZ male/ZW female sex-determining system of birds, dosage compensation for Z-linked genes does not occur by inactivation of one of the two Z chromosomes in the homogametic male. The heterochromatic W chromosomes of the three species showed bright labeling with distamycin A/mithramycin counterstain-enhanced fluorescence and exhibited significantly delayed DNA replication. The nucleolus organizers of birds, frequently located in microchromosomes, were also distinguished by bright distamycin A/mithramycin fluorescence.     

Chromosomes of a cell line of Dipodomys panamintinus (kangaroo rat) a banding and autoradiographic study

The chromosomes of an established cell line of Dipodomys panamintinus have been characterised in terms of their C, G and Q banding patterns, and the distributions of silver grains in autoradiographs of chromosomes labelled in early or late S phase. No relationship could be established between C, G or Q banding regions of chromosomes and a particular S phase time of replication of the DNA in these banded regions. The implication of this result to the concept of heterochromatin is discussed.     

Chromosome studies on a human liposarcoma cell line.

Numerical and structural chromosome analysis of a human retroperitoneal liposarcoma cell line maintained under standard cell culture conditions revealed a very stable hypodiploid mode. If the cells were not trypsinized for several generations, a near-triploid stemline, which was generally a duplication of the hypodiploid mode, emerged. Some chromosomes appeared to be relatively stable pairs (1, 2, 7, 9, and 12), but most had "lost" one homolog or both (4 and 21) or were rearranged into "new" marker chromosomes. Quantitation of the genetic material showed a loss of 12.0 +/- 3.7% per spread. Only one characteristically long marker chromosome, which is present in every cell, could be identified with certainty as a translocation between chromosomes 4 and 11. Several of the marker chromosomes showed interstitial negatively staining regions with the trypsin-Giemsa method.     

Perturbation analysis of competition and overlap in habitat utilization between Dipodomys ordii and Dipodomys merriami

Summary The populations of two coexisting species of Dipodomys (Heteromyidae, Rodentia) were manipulated on 10, large, unenclosed, trapping grids. These manipulations revealed that, although many kangaroo rats are established residents in an area, a large number are transient individuals who quickly occupy vacated habitats. On plots from which residents had been removed, transients settled at rates of up to 5% of carrying capacity per day. These immigrants were invariably of the same species that was removed, indicating a strong element of intraspecific competition with little or no evidence of competition between the species.Trapping records suggest that these species avoid competition through habitat selection. Dipodomys ordii prefer a grassier habitat, and D. merriami a habitat dominated by creosote bush. Apparent overlap in their utilization of habitats, based on sites of capture, predicts competition coefficients to be higher than those permitted by the theory of limiting similarity and much higher than those actually shown by the perturbation experiments.This study demonstrates the dangers of estimating alpha without experimentation. This is especially true in cases where habitat selection may be important, since organisms may travel in habitats without collecting resources therein. Our results are discussed in light of a theory which examines the optimal (rather than tolerable) amount of overlap in habitat utilization between two potential competitors in a mixed habitat. This theory predicts that the pressure of natural selection should eliminate the interspecific competition entirely.However, the conclusion that the interspecific competitive alpha is zero does not lead to the conclusion that interspecific competition is unimportant in the system. Instead, if our interpretation is correct, such competition has molded the system, and were there not a continual threat of interspecific competition, the habitat specializations would soon disappear.     

Neighbor Recognition in a Solitary Desert Rodent (Dipodomys merriami)

Neighbor recognition in the Merriam's kangaroo rat (Dipodomys merriami) was tested in neighbor and nonneighbor pairs of the same and opposite sex in a large enclosure in the field. Mutual tolerance, rather than aggression, occurred in the encounters, and neighbor recognition was more apparent in females than in males. Females tolerated and engaged in nonagonistic contact with familiar males and females; males approached and attempted to contact neighbors and nonneighbors alike. Neighbor recognition is important to both spacing and mating in females. Males' persistent attempts to interact with any conspecific may be important to their mating success.     

Chromosome banding in Amphibia. XXVII. DNA replication banding patterns in three anuran species with greatly differing genome sizes

The mitotic chromosomes of three anuran species, Scaphiopus holbrooki, Litoria infrafrenata and Odontophrynus americanus, were analyzed by means of the 5-bromodeoxyuridine/deoxythymidine (BrdU/dT) replication banding technique. These species exhibit large differences in their genome sizes: S. holbrooki possesses one of the smallest genomes among vertebrates, L. infrafrenata has a genome size near the modal DNA value of most Amphibia, whereas O. americanus is a tetraploid species. BrdU/dT labeling induces reproducible and reliable R- and G-replication bands along the metaphase chromosomes of all three species. Irrespective of the genome size of the species considered, the number of early (R-) and late (G-) replicating bands per haploid karyotype is nearly the same. The chromosomes of the autotetraploid O. americanus can be arranged into sets of four homologous chromosomes (quartets). C-bands and BrdU/dT replication bands reveal heterogeneity within the quartets 1, 3 and 4 that are interpreted as the initiation of a diploidization process.     

Unappreciated tolerance to high ambient temperatures in a widely distributed desert rodent, Dipodomys merriami

A long-held assertion has been that nocturnality is an escape mechanism for many nocturnal desert rodents because of limited tolerances to heat. To test this claim, we used a treadmill to examine the tolerances to high ambient temperatures (T(a)'s) of one subspecies of desert rodent, Merriam's kangaroo rat, Dipodomys merriami merriami, from contrasting environments. We simultaneously measured body temperature (T(b)), evaporative water loss, and metabolic rates at an ecologically relevant speed (0.6 km h(-1)) at different ambient temperatures (Ta=25 degrees -42.5 degrees C). We hypothesized that kangaroo rats from a more xeric site would have greater abilities to remain active and maintain stable T(b) than those from a more mesic site, but mesic- and xeric-site animals had comparable tolerances and were active until Tb=42 degrees C. At Ta=42.5 degrees C, however, T(b) of mesic-site animals increased more quickly than in xeric-site animals. Although most animals could not run more than 18 min at Ta=42.5 degrees C, most could run at Ta=40 degrees C for at least 30 min. Benefits of nocturnality for this species may reside more in purposes of water conservation and avoidance of predation and less on the direct regulation of T(b), as T(b) is more labile than commonly thought.     

Behavioural syndromes in Merriam's kangaroo rats (Dipodomys merriami): a test of competing hypotheses

Behavioural syndromes, correlations of behaviours conceptually analogous to personalities, have been a topic of recent attention due to their potential to explain trade-offs in behavioural responses, apparently maladaptive behaviour and limits to plasticity. Using Merriam's kangaroo rats (Dipodomys merriami), we assessed the explanatory power and generality of hypothesized syndrome structures derived from the literature and the natural history of the species. Several aspects of functionally distinct behavioural responses of D. merriami were quantified. Syndrome structures were compared using structural equation modelling and model selection procedures. A domain-general behavioural syndrome incorporating cross-functional relationships between measures of boldness, agonistic behaviour, flexibility and food hoarding best explained the data. This pattern suggests that D. merriami behaviours should not be viewed as discrete elements but as components of a multivariate landscape. Our results support arguments that a lack of independence between behaviours may be a general aspect of behavioural phenotypes and suggest that the ability of D. merriami's behaviour to respond to selection may be constrained by underlying connections.     

Chromosome banding and compaction

Summary We have described a characteristic substructure of mitotic chromosomes, the chromosomal unit fibre, with lengths about five times the length of the corresponding metaphase chromosomes and a uniform diameter of 0.4 m. In order to study the relationship of chromosome banding to chromosome compaction, methods have been devised to obtain banding patterns on chromosomal unit fibres, similar to G-band patterns of intact mitotic chromosomes. The total number of bands plus interbands per haploid human karyotype is estimated at about 3000. The banding pattern of chromosomal unit fibres indicates a certain resemblance to the normal G-banding pattern of human chromosomes even if the details indicate a short-range random distribution.     

Scatter hoarding by kangaroo rats (Dipodomys merriami) and pilferage from their caches

We observed radio-implanted Merriam's kangaroo rats disposingof 10-g bonanzas of rolled oats in 48 trials in the field. Theprincipal determinant of the initial disposition of discoveredfood was apparently its distance from the day burrow: food foundwithin about 10m was mainly larder hoarded, whereas food encounteredfarther afield was usually dispersed immediately in shallowcaches. Cache sites were newly dug for the purpose and not reused;most caches were nearer the current day burrow than was thefood source, but a few were placed far from both the cacher'sday burrow and its habitual nocturnal range. An experiment withartificial caches indicated that security from discovery increaseswith spacing and with proximity to perennial shrubs. Nine kangaroorats cached dyed food, and fecal dye traces revealed extensivepilferage from five of them, by both conspecifics and otherrodent species. Limited evidence indicates that food encounterednearer home and initially larder hoarded was more secure frompilferage than food initially scattered, and yet kangaroo ratswere observed to scatter caches soon after initial larder hoarding.A kangaroo rat whose dyed stores escaped pilferage fed fromthem at intervals for at least 12 days. Even cachers who incurredpilferage made as much, or more, use of their caches as anythief, suggesting that scattering caches may be a defense againstcatastrophic losses.     

Effects of food value, predation risk, and pilferage on the caching decisions of Dipodomys merriami

Animals that scatter cache their food face a trade-off betweenthe benefits of protecting caches from pilferers and the costsassociated with caching. Placing food into a large number ofwidely spaced caches helps to protect it from pilferage butalso involves costs such as greater exposure to predators. Ipredicted that animals would disperse food into a larger numberof more widely spaced caches when caching (1) a preferred foodversus a less preferred food and (2) under conditions of lowpredation risk versus high predation risk. To test these predictions,I examined the scatter-caching decisions of Merriam's kangaroorats (Dipodomys merriami). D. merriami distributed caches inclumped patterns, regardless of food preference, but they showeda tendency to invest more in a preferred food by distributingcaches more widely. Under the relative safety of the new moon,they did not disperse caches more widely, rather they partitionedthe same amount of food into a larger number of caches thanthey did under the full moon, when predation risk is higher.To examine whether their cache spacing decisions had a significantimpact on the success of cache pilferers, I measured discoveryby pilferers of artificial caches of two food types at differentcaching distances. Results indicate that the cache spacing behaviorof D. merriami functions to protect caches from pilferers, becauseincreased spacing of artificial caches decreased the probabilityof pilferage for both types of food.     

Chromosome banding studies by replication and restriction enzyme treatment in vendace (Coregonus albula) (Salmonidae, Salmoniformes)

Chromosome banding studies were performed in vendace, Coregonus albula. Original data on distribution of early and late replication regions, restriction sites (AluI, DdeI, HinfI and HaeIII) on chromosomes in this coregonid fish have been used to analyse karyotype heterochromatin differentiation. Heterochromatic bands (C-positive and not digested by restriction enzymes) have been identified as late replicating regions. Extra bands produced by the applied methods have permitted the identification of several homologous pairs. The centromeres were differentially digested by the restriction enzymes. The studied population seems to be homogenic regarding karyotype characteristics.