Structural heterogeneity in the basal regions of the teeth of the red-backed salamander,Plethodon cinereus (Amphibia,Plethodontidae)

Ultrastructural and histochemical features of marginal (monostichous) teeth associated with the jawbones are compared with those of palatal (polystichous) teeth that compose two patches in the roof of the mouth. The apices and uncalcified regions are similar in both kinds of teeth, but the basal regions display distinctive differences. While bases (pedestals) of marginal teeth are essentially hollow cylinders that attach to the jawbones by their labial faces, bases of teeth in palatal patches are fused to form two horizontal plates which lack direct attachment to underlying bone. The plates are separated from each other by a pulp-filled space containing fibroblasts, blood vessels, and vertically oriented elements resembling bony spicules. Cylindrical pedestals like those of marginal teeth project from the ventral plate. While the identity of the material composing the basal regions remains controversial, the following evidence suggests that it is similar to “bone of attachment” (Tomes, '23): most of it, unlike dentin, does not develop in direct association with an enamel organ; alcian blue stains the bases of developing teeth but stains dentin, developing dentin, enamel, or mature bone very weakly (if at all); bases of teeth in palatal patches develop in isolation from the parasphenoid bone and thus cannot be considered extensions of it; and marginal teeth attach directly to the jawbones, but the material composing their bases does not blend with the bone. Structural heterogeneity of the basal regions appears to be linked to functional differences exhibited by these two types of teeth.     

The jamming avoidance response in gymnotoid pulse-species: A mechanism to minimize the probability of pulse-train coincidence

Summary Gymnotoid electric fish with pulse-type electric organ discharges (EODs) shorten (lengthen) their EOD intervals as pulses of a slightly slower (faster) train scan their EODs (Figs. 1, 2). They thus minimize the chance of pulse coincidence by transient accelerations (decelerations) of their EOD rate.Studies in curarized preparations demonstrate that this Jamming Avoidance Response (JAR) is controlled by electroreceptive input alone and without reference to an internal electric organ pacemaker-related signal (Fig. 8). A sufficient stimulus input consists of a train of strong, EOD-like stimulus pulses (S₁), which mimic the animal's experience of its own EOD, and a train of small pulses (S₂) of slightly different repetition rate, which mimic EODs of a neighbor. Correct behavioral responses require S₁ pulses of sufficient intensity to recruit pulse-markertype receptors; also spatial and temporal patterns must closely resemble those of the animal's EOD. These features are of little significance for S₂ pulses which, while scanning S₁ pulses, only provide a small perturbation of electroreceptive feedback from S₁ pulses. Inappropriate S₁ stimulation impairs and sometimes reverses (Fig. 7) the behavioral discrimination of scan directions. The JAR is explained in terms of excitatory and inhibitory processes (Fig. 3) which are triggered by S₂ stimulation, at specific phases within the S₁ cycle (Figs. 4–6).The JAR in pulse species strongly resembles the JAR in wave-species (Bullock et al., 1972) and could be considered an evolutionary ancestor of the latter. It is a response to a particular novelty in electroreceptive feedback.We thank Drs. T.H. Bullock, C. Hopkins and an anonymous referee for most helpful criticism. This research was supported by NSF grand BMS74-18640 and NIMH grant PHSMH-2614901 to W.H. and NIH grant/ROI NS 12337-01 to J.B.     

Periapical abscesses of cut canine teeth in cynomolgus macaques

Periapical abscesses of canine teeth in a group of 47 male cynomolgus macaques are found to be associated with a procedure, involving cutting the canine teeth, used to make non-human primates less hazardous. Examination of 150 canine teeth in dry specimens revealed 30 cut teeth with no exposure of the pulpal chamber and 107 cut teeth where the dental pulp had been exposed. Of those teeth which had the pulpal chamber exposed by the cutting procedure, 85 (79.4%) showed clear evidence of osseous changes consistent with abscess formation in the apical regions.     

Exposure to noise pollution across North American passerines supports the noise filter hypothesis

The noise filter hypothesis predicts that species using higher sound frequencies should be more tolerant of noise pollution, because anthropogenic noise is more intense at low frequencies. Recent work analysed continental‐scale data on anthropogenic noise across the USA and found that passerine species inhabiting more noise‐polluted areas do not have higher peak song frequency but have more complex songs. However, this metric of song complexity is of ambiguous interpretation, because it can indicate either diverse syllables or a larger frequency bandwidth. In the latter case, the finding would support the noise filter hypothesis, because larger frequency bandwidths mean that more sound energy spreads to frequencies that are less masked by anthropogenic noise. We reanalysed how passerine song predicts exposure to noise using a more thorough dataset of acoustic song measurements, and showed that it is large frequency bandwidths, rather than diverse syllables, that predict the exposure of species to noise pollution. Given that larger bandwidths often encompass higher maximum frequencies, which are less masked by anthropogenic noise, our result suggests that tolerance to noise pollution might depend mostly on having the high‐frequency parts of song little masked by noise, thus preventing acoustic communication from going entirely unnoticed at long distances.     

Genomic and phenotypic effects of inbreeding across two different hatchery management regimes in Chinook salmon

Genomic approaches permit direct estimation of inbreeding and its effect on fitness. We used genomic‐based estimates of inbreeding to investigate their relationship with eight adult traits in a captive‐reared Pacific salmonid that is released into the wild. Estimates were also used to determine whether alternative broodstock management approaches reduced risks of inbreeding. Specifically, 1,100 unlinked restriction‐site associated (RAD) loci were used to compare pairwise relatedness, derived from a relationship matrix, and individual inbreeding, estimated by comparing observed and expected homozygosity, across four generations in two hatchery lines of Chinook salmon that were derived from the same source. The lines are managed as “integrated” with the founding wild stock, with ongoing gene flow, and as “segregated” with no gene flow. While relatedness and inbreeding increased in the first generation of both lines, possibly due to population subdivision caused by hatchery initiation, the integrated line had significantly lower levels in some subsequent generations (relatedness: F₂–F₄; inbreeding F₂). Generally, inbreeding was similar between the lines despite large differences in effective numbers of breeders. Inbreeding did not affect fecundity, reproductive effort, return timing, fork length, weight, condition factor, and daily growth coefficient. However, it delayed spawn timing by 1.75 days per one standard deviation increase in F (~0.16). The results indicate that integrated management may reduce inbreeding but also suggest that it is relatively low in a small, segregated hatchery population that maximized number of breeders. Our findings demonstrate the utility of genomics to monitor inbreeding under alternative management strategies in captive breeding programs.