Zeitschrift für vergleichende Physiologie

We present a quantitative mathematical model that represents the main features of the bullfrog inner ear. Calculated responses based on this model predict the observed frequency separation between the amphibian papilla and basilar papilla responses. The origin of this separation can be traced to the effect of the contact membranes on the impedance of the respective paths. Additionally, we calculated the input impedance of the periotic canal and showed that at low frequencies it acts as a bypass for most of the energy entering the ear, shunting it away from the amphibian-basilar papilla complex. As this shunting decreases with increasing frequency, we propose that the periotic canal functions as a protection mechanism to prevent overload of the amphibian papilla and basilar papilla during ventilation and for quasi-static pressure equalization. Our model explains the main features of the empirical data obtained from direct measurement of the amphibian papilla and basilar papilla contact membranes reported in an accompanying paper (this issue).

The ultrastructure and major soluble proteins of the transparent eye lens of two cubomedusan jellyfish,Tripedalia cystophora andCarybdea marsupialis, have been examined. Each species has two complex eyes (one large and one small) on four sensory structures called rhopalia. The lenses consist of closely spaced cells with few organelles. The lens is situated next to the retina, with only an acellular layer separating it from the photoreceptors. SDS-PAGE showed that the large lens ofC. marsupialis has only two crystallin polypeptide bands (with molecular masses of approximately 20000 and 35000 daltons), while that ofT. cystophora has three bands (two with a molecular mass near 20000 daltons and one with a molecular mass near 35000 daltons). Interestingly, the small lens ofT. cystophora appears to be markedly deficient in or lack the lower molecular weight proteins. The crystallins behaved as monomeric proteins by FPLC and showed no immunological reaction with antisera of the major squid crystallin, chickenδ-crystallin or mouseγ-crystallin in western immunoblots. Very weak reactions were found with antimouseα- andβ-crystallin sera. The 35000 dalton crystallin ofT. cystophora was purified and called J1-crystallin. It contained relatively high leucine (13%) and tyrosine (9%) and low methionine (2%). Several tryptic peptides were sequenced. Weak sequence similarities were found withα- andβ-crystallins, which may account for some of the apparent weak immunological crossreactivity with these vertebrate crystallins. A polyclonal antiserum made in rabbits from a synthetic peptide of J1-crystallin reacted strongly with J1-crystallin ofT. cystophora andC. marsupialis in immunoblots; by contrast, no reaction was obtained with the lower molecular weight crystallins from these jellyfish, with the squid crystallin, or with any crystallins from the frog or human lens. Thus, despite the structural similarities between the cubomedusan, squid and vertebrate lenses, their crystallins appear very different.

The homology between the avian hippocampal formation (HF) and mammalian hippocampus nurtures the expectation that HF plays a fundamental role in navigation by migratory birds. Indeed, HF of migratory birds displays anatomical properties that differ from non-migratory species. Using a hypothetical framework of multiple maps of differing spatial resolution and range, homing pigeon data suggest that HF is important for navigating by landscape features near familiar breeding, over-wintering, and stop-over sites. By contrast, HF would be unimportant for an olfactory navigational map, which could be operational over unfamiliar space farther away from a goal location, nor is there any evidence for HF involvement in the sun or geomagnetic compass. The most intriguing question that remains open is what role HF may play in navigation when a migrant is thousands kms away from a familiar area, where homing pigeon data are uninformative and a geomagnetic map may be operational. Beyond navigation, successful migration depends on seasonal timing and often becoming nocturnally active. There is little evidence that HF plays a role in the timing of circannual and circadian cycles. Rather, circadian pacemakers including the pineal gland may control circadian timing of nocturnal restlessness and photoperiodic seasonal pacemakers likely control circannual expression.

We have studied the escape-swimming behavior and neurophysiology ofTritonia hombergi and compared it with another species,Tritonia diomedia in an effort to determine some of the neurophysiological correlates of the modifications in the behavior brought upon by evolution. The general form of the responses in the two species is similar. However, there are well-defined differences in the facility with which the response can be elicited, and in the parameters of response duration over repeated trials (Fig. 2).T. hombergi has many neurons that are homologous in terms of relative size, pigmentation, location and function when compared toT. diomedia (Fig. 3). We attribute the reduced probability of initiation of escape-swimming inT. hombergi to specific alterations in the condition of the central neurons (TGN's) responsible for triggering it. It was found that; (i) these neurons produce weaker responses to appropriate stimuli (Fig. 4), (ii) there are substantially fewer such neurons and, (iii) there are neurons on the margins of the group with reduced regenerative firing capabilities (Fig. 5). Since the TGN's are electrically coupled to these latter neurons, it is suggested that the regenerative excitability of the TGN system as a whole is reduced by the loading effect of these less excitable neurons. It is proposed that the TGN system and consequently the escape-swimming response ofT. hombergi are in a transitional state in evolutionary terms. The small size of the TGN group and its interactions with nearby neurons are consistent with the idea that it is either recruiting or losing efficacy as the adaptive value of the behavior changes.