The influence of photoperiod and genotype on thermal preference of juvenile Gryllus firmus was explored. Both rearing condition and genotype affect temperature preference. The following results were obtained: (1) the wing morph of juveniles raised at 28$ sp circ$C 16hL:8hD is determined before 20 days post hatching. (2) Crickets distribute themselves on the apparatus differently in the presence of a thermal gradient than in its absence: such controls for positioning preference are rare in the literature. (3) Juveniles younger than 20 days old tend to choose higher surface temperatures and achieve higher body temperatures if either rearing photoperiod or selection predisposes them to microptery and choose lower temperatures if they are predisposed towards macroptery. (4) The differences in thermal preference between presumptive macropters and micropters remains significant after differences in body size are taken into account. The differences in thermal preference could act as a novel mechanism for lowering the heritability of wing morph.

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Crickets provide a useful model system to study how animals analyze sound frequency. While much is known about how sound frequency is represented by central neurons and in behavior, little is yet known about auditory receptor neurons. I investigated physiological and anatomical properties of auditory receptor fibers (ARFs) and functional organization of their axon terminals, using single-unit recording and staining techniques. Behavioral experiments suggest that crickets are sensitive to two broad frequency ranges, centered at 4--5 kHz for acoustic communication and at 25--50 kHz for predator detection. However, cricket ARFs fall into three distinct populations, based on characteristic frequency (CF; low frequency, ∼3--5.5 kHz; mid frequency, 9--12 kHz; ultrasound, ≥18 kHz). One striking characteristic of single ARFs is the occurrence of multiple sensitivity peaks at different frequencies, which implies that the wide audible range of crickets is mediated by these multiple sensitivity peaks, even though CFs of ARFs are clustered at the three small ranges. To understand how populations of ARFs code sound intensity, level-response functions are examined. Physiological parameters derived from level-response functions are diverse, and are systematically related to threshold within each population. Low-frequency ARFs comprise two distinct anatomical types, based on the distributions of axon terminals, which also differ physiologically. Thus, based on CF and anatomy, cricket ARFs can be classified into four distinct populations. To understand how information flows from peripheral to central neurons, the positions of varicosities, i.e. output sites, of ARF axon terminals are mapped on a two-dimensional coordinate system. In crickets, the ARF axon terminals are functionally organized with respect to frequency and intensity. Anatomical organization with respect to threshold is related to physiological organization, which may reduce non-linear effects in postsynaptic

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