I. the origin of species by means of natural selection

World wheat grain yields increased substantially in the 1960s and 1970s because farmers rapidly adopted the new varieties and cultivation methods of the so-called 'green revolution'. The new varieties are shorter, increase grain yield at the expense of straw biomass, and are more resistant to damage by wind and rain. These wheats are short because they respond abnormally to the plant growth hormone gibberellin. This reduced response to gibberellin is conferred by mutant dwarfing alleles at one of two Reduced height-1 (Rht-B1 and Rht-D1) loci. Here we show that Rht-B1/Rht-D1 and maize dwarf-8 (d8) are orthologues of the Arabidopsis Gibberellin Insensitive (GAI) gene. These genes encode proteins that resemble nuclear transcription factors and contain an SH2-like domain, indicating that phosphotyrosine may participate in gibberellin signalling. Six different orthologous dwarfing mutant alleles encode proteins that are altered in a conserved amino-terminal gibberellin signalling domain. Transgenic rice plants containing a mutant GAI allele give reduced responses to gibberellin and are dwarfed, indicating that mutant GAI orthologues could be used to increase yield in a wide range of crop species.

‘Green revolution’ genes encode mutant gibberellin response modulators

We have traced central nervous pathways controlling bird son in the canary using a combination of behavioral and anatomical techniques. Unilateral electrolytic brain lesions were made in adult male canaries whose son had been previously recorded and analysed on a sound spectrograph. After severral days of postoperative recording, the birds were sacrificed and their brains processed histologically for degeneration staining with the Fink-Heimer technique. Although large lesions in the neostriatum and rostral hyperstriatum had no effect on song, severe song deficits followed damage to a discrete large-celled area in the caudal hyperstriatum ventrale (HVc). Degenerating fibers were traced from this region to two other discrete nuclei in the forebrain: one in the parolfactory lobe (area X, a teardrop-shaped small-celled nucleus) and a round large-celled nucleus in the archistriatum (RA). Unilateral lesions of X had no effect on song; lesions of RA, however, caused severe song deficits. Degenerating fibers from RA joined the occipitomesencephalic tract and had widespread ipsilateral projections to the thalamus, nucleus intercollicularis of the midbrain, reticular formation, and medulla. It is of particular interest that direct connections were found onto the cells of the motor nucleus innervating the syrinx, the organ of song production. Unilateral lesions of n. intercollicularis (previously implicated in the control of vocal behavior) had little effect on song.



One bilateral lesion of HVc resulted in permanent (9 months) and complete elimination of the audible components of song, although the bird assumed the posture and movements typical of song. Preliminary data suggest that lesions of the left hemisphere result in greater deficits than lesions of the right one. This finding is consistent with earlier reports that the left syrinx controls the majority of song components. Results reported here suggest a localization of vocal control in the canary brain with an overlying left hemispheric dominance.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/cne.901650405

Central control of song in the canary, Serinus canarius

Recent improvements in genetic analysis and genotyping methods have resulted in a rapid expansion of the power of molecular markers to address ecological questions. Microsatellites have emerged as the most popular and versatile marker type for ecological applications. The rise of commercial services that can isolate microsatellites for new study species and genotype samples at reasonable prices presents ecologists with the unprecedented ability to employ genetic approaches without heavy investment in specialized equipment. Nevertheless, the lack of accessible, synthesized information on the practicalities and pitfalls of using genetic tools impedes ecologists ability to make informed decisions on using molecular approaches and creates the risk that some will use microsatellites without understanding the steps needed to evaluate the quality of a genetic data set. The first goal of this synthesis is to provide an overview of the strengths and limitations of microsatellite markers and the risks, cost and time requirements of isolating and using microsatellites with the aid of commercial services. The second goal is to encourage the use and consistent reporting of thorough marker screening to ensure high quality data. To that end, we present a multistep screening process to evaluate candidate loci for inclusion in a genetic study that is broadly targeted to both novice and experienced geneticists alike.

Microsatellites for ecologists: a practical guide to using and evaluating microsatellite markers

Developmental Plasticity and Evolution. In: Mary Jane West-Eberhard, Editor, Oxford University Press (2003) Pp. xi+794. Price $50.00 paper.

Electroreceptive neurons in the posterior branch of the anterior lateral line nerve of three species of electric fish (Gymnotoidei):Sternopygus macrums, Eigenmannia virescens, andApteronotus albifrons, show speciesspecific differences in the filtering of electrical stimuli. All of the tuberous electroreceptor fibers of an individual are tuned to the same frequency: that of the electric organ discharge (EOD) of the species, more specifically, to that of the individual. The fibers inSternopygus are tuned to 50–150 Hz; those inEigenmannia to 250–500 Hz, and those inApteronotus to 800–1,200 Hz (Figs. 3, 5, 8). Two classes of organs inSternopygus andEigenmannia, P and T units, respond to sinusoidal stimuli at the unit's best frequency (BF) with a phase-locked partially-adapting (P), or tonic (sustained) (T) discharge. T-units are more sharply tuned and are more sensitive than P-units. Only one class of organs,P or partially adapting units, have been found inApteronotus and phase-locking is less evident than it is in other species.

Stimulus Filtering and Electroreception: Tuberous Electroreceptors in Three Species of Gymnotoid Fish

An electric fish in the African family Mormyridae recognizes members of its own species by "listening" to electric organ discharges, which are species-specific signatures. Reactions of fish in the field and of individual electroreceptors to both normal and modified computer-synthesized discharges emphasize the importance of the waveform (time-domain cues) in species recognition.

https://science.sciencemag.org/content/sci/212/4490/85.full.pdf

Temporal Coding of Species Recognition Signals in an Electric Fish

Eigenmannia virescens was observed in aquaria in Guyana, South America, during the non-breeding and breeding seasons. Agonistic behavior was described and correlated with electrical activity. Variations in the electric discharges play important roles in agonistic behavior as displays given during attack and retreat. Although descriptions of sexual behavior are not complete, certain electrical signals also appear to be used in courtship. The role of electrical signals in agonistic behavior of Eigemnannia were studied by (1) an analysis of the behavior of fish in dominant and subordinate roles, (2) an analysis of the simultaneous occurrence of electrical displays and motor actions, (3) an analysis of preceding actions of one fish and following actions of the other fish, and (4) analysis of responses to artificial electrical stimuli. These studies indicate that at least three classes of electric signals are important in communication among Eigenmannia: the normal discharge, Interruptions, and Rises. The normal discharge. The normal discharge of Eigenmannia virescens is species-distinctive in the area where this study was conducted. Playback of recorded signals and presentation of sinusoidal electrical stimuli, indicates that the normal discharge particularly the fundamental frequency of the normal discharge (240 to 600 Hz)- is used in species recognition. Males and females overlap extensively in their discharge frequency, and males do not appear to distinguish the electric discharges of males from those of females. Interruptions. Interruptions are brief cessations of the electric discharge. They are most often 20 to 40 msec in duration during agonistic interactions whereas they are often 60 to 80 msec when given by males during interactions with females during the breeding season. Interruptions are usually given in bouts where a bout is any group of Interruptions separated by less than 1.5 seconds. Interruptions are given almost exclusively by dominant fish. They are given at the same time as Attacks, Threats, and No Action, but rarely during Retreat. Bouts with many Interruptions are more likely to be associated with Attacks, and less likely with No Action, than are bouts containing only a few Interruptions. Interruptions correlate with motivation to Attack, and the number of Interruptions in a bout correlates with the probability of attack. Interruptions in one fish are followed by Retreat and No Action in the other fish, thus they appear to be an effective threat display. Interruptions with long durations are given at high repetition rates by male Eigenmannia in the presence of females during the breeding season, thus they may play a role in courtship. Rises. A Rise is an increase in discharge frequency followed by a decrease to the resting frequency. Rises lasting less than two seconds (Short Rises) are often given by dominant fish in agonistic interactions, most often at the same time as Attacks or Threats. They are given rarely. Long Rises (longer than two seconds) are given predominantly by subordinate fish in agonistic interactions. They are given simultaneous with Retreat and No Action and are thus an indicator of submissive behavior. Long Rises in one fish are followed by Attacks, Threats, Approaches, and by No Action in the other. During the breeding season, females, in the presence of males, often give long series of frequency modulations of unknown significance.

Electric Communication: Functions in the Social Behavior of Eigenmannia Virescens

Natural selection arising from resource competition and environmental heterogeneity can drive adaptive radiation. Ecological opportunity facilitates this process, resulting in rapid divergence of ecological traits in many celebrated radiations. In other cases, sexual selection is thought to fuel divergence in mating signals ahead of ecological divergence. Comparing divergence rates between naturally and sexually selected traits can offer insights into processes underlying species radiations, but to date such comparisons have been largely qualitative. Here, we quantitatively compare divergence rates for four traits in African mormyrid fishes, which use an electrical communication system with few extrinsic constraints on divergence. We demonstrate rapid signal evolution in the Paramormyrops species flock compared to divergence in morphology, size, and trophic ecology. This disparity in the tempo of trait evolution suggests that sexual selection is an important early driver of species radiation in ...

/pdf/sexual-signal-evolution-outpaces-ecological-divergence-e2yuto3704.pdf

Sexual Signal Evolution Outpaces Ecological Divergence during Electric Fish Species Radiation

How do the communication discharges produced by electric fish evolve to accommodate the unique design features for the modality? Two design features are considered: first, the limited range of signaling imposed on the electric modality by the physics of signal transmission from dipole sources; and second, the absence of signal echoes and reverberations for electric discharges, which are non-propagating electrostatic fields. Electrostatic theory predicts that electric discharges from fish will have a short range because of the inverse cube law of geometric spreading around an electrostatic dipole. From this, one predicts that the costs of signaling will be high when fish attempt to signal over a large distance. Electric fish may economize in signal production whenever possible. For example, some gymnotiform fish appear to be impedance-matched to the resistivity of the water; others modulate the amplitude of their discharge seasonally and diurnally. The fact that electric signals do not propagate, but exist as electrostatic fields, means that, unlike sound signals, electric organ discharges produce no echoes or reverberations. Because temporal information is preserved during signal transmission, receivers may pay close attention to the temporal details of electric signals. As a consequence, electric organs have evolved with mechanisms for controlling the fine structure of electric discharge waveforms.

Carl Hopkins

Papers

Stimulus Filtering and Electroreception: Tuberous Electroreceptors in Three Species of Gymnotoid Fish

Temporal Coding of Species Recognition Signals in an Electric Fish

Electric Communication: Functions in the Social Behavior of Eigenmannia Virescens

Sexual Signal Evolution Outpaces Ecological Divergence during Electric Fish Species Radiation

Design features for electric communication.