Biology subjects

Liddle, T. A.

Publications and source records attributed to Liddle, T. A..

4 recordsLinked to original sources

bioRxiv2025

Breeding Males, But Not Females, Have Elevated Androgen Receptor Expression in the Northern House Wren (Troglodytes Aedon), a Temperate Songbird with Female Song

In many male temperate-breeding songbirds, increased plasma testosterone in the early breeding season regenerates song control nuclei that regulate song. Females of some temperate species also sing but have lower circulating testosterone concentrations. We hypothesized that upregulation of steroid receptors in females could compensate for low circulating testosterone, focusing on the northern house wren (Troglodytes aedon), a temperate-breeding songbird in which both sexes sing. We collected brain tissue from both sexes during the early breeding, late breeding, and nonbreeding season. Using quantitative PCR, we quantified mRNA expression of four genes--androgen receptor (AR), estrogen receptors (ER and ER{beta}), and aromatase (AROM)--in three song nuclei--HVC, Area X, and RA--and compared sexes. We found females had lower expression than males of AR, AROM and ER in most song nuclei, especially of AR in HVC in the breeding season. Both sexes, however, had low ER expression in Area X and RA. In males, expression differed seasonally: breeding males had higher expression of AR in RA and AROM in HVC than nonbreeding males. In both sexes, expression differed among song nuclei: in most genes, HVC had the highest expression, followed by RA, then Area X. These findings suggest singing female house wrens do not compensate for low plasma testosterone by upregulating steroid receptors beyond male levels or during early breeding, when they sing most. Conversely, increased AR expression in breeding males indicates differences in the mechanisms regulating male and female song, with testosterone playing a greater role in male birdsong.

animal behavior and cognition↗

bioRxiv2025

Seasonal neurogenomic changes provide genetic links between male song and testosterone-mediated neurogenesis in a wild songbird

Seasonal changes in testosterone mediate the transition from reduced singing in the non-breeding season to high song rates in the early breeding season in male temperate songbirds, a process accompanied by marked neurogenesis in song control regions of the brain. However, the resulting genetic changes and their association with the subsequent behavioral, neuroanatomical and reproductive changes remain poorly understood. Here, we compared gene expression in HVC, a major song control nucleus, between the non-breeding and breeding season in male northern house wrens (Troglodytes aedon) and we examined associations with HVC volume, plasma testosterone concentrations, and testes size. Differential gene expression analysis identified three genes (CLIP4, FAM169A, and TTR) consistently linked to seasonal transitions from non-breeding to three breeding stages (pre-laying, egg-laying and incubation). Notably, TTR, which transports thyroid hormone (TH), was highly expressed in the nonbreeding season, consistent with a possible role of TH in regulating seasonal shifts in song output and structure. We also identified seasonal changes in networks of genes related to neural connectivity, cellular restructuring, and cell migration. Weighted gene co-expression network analysis (WGCNA) revealed gene clusters specifically correlated with testosterone and HVC volume. Testosterone-associated genes included genes involved in neural circuit remodeling, chromatin organization, and cytoskeletal dynamics, consistent with testosterone-mediated regulation of these neuroanatomical changes. Genes linked to seasonal increases in HVC volume were involved in neuronal restructuring and neuron migration, implicating these genes in seasonal neurogenesis. Together, our findings link novel gene expression patterns to hormone regulation and neurogenesis underlying seasonal transitions in birdsong.

genomics↗

bioRxiv2025

Hypothalamic deiodinase type-3 establishes the period of circannual interval timing in mammals

Animals respond to environmental cues to time phenological events, but the intrinsic mechanism of circannual timing remains elusive. We used transcriptomic sequencing and frequent sampling of multiple hypothalamic nuclei in Djungarian hamster to examine the neural and molecular architecture of circannual interval timing. Our study identified three distinct phases of transcript changes, with deiodinase type-3 (Dio3) expression activated during the early induction phase. Subsequent work demonstrated that targeted mutation of Dio3 using CRISPR-Cas resulted in a shorter period for circannual interval timing. Hamsters that are non-responsive to short photoperiod and fail to show any winter adaptations do not display changes in Dio3 expression do not show any change in body mass or pelage. Our work demonstrates that changes in Dio3 induction is essential for setting the period of circannual interval timing.

neuroscience↗

bioRxiv2023

FSHβ links photoperiodic signalling to seasonal reproduction in Japanese quail

Annual cycles in daylength provide an initial predictive environmental cue that plants and animals use to time seasonal biology. Seasonal changes in photoperiodic information acts to entrain endogenous programs in physiology to optimize an animals fitness. Attempts to identify the neural and molecular substrates of photoperiodic time measurement in birds have, to date, focussed on blunt changes in light exposure during a restricted period of photoinducibility. The objectives of these studies were first to characterise a molecular seasonal clock in Japanese quail and second, to identify the key transcripts involved in endogenously generated interval timing that underlies photosensitivity in birds. We hypothesized that the mediobasal hypothalamus (MBH) provides the neuroendocrine control of photoperiod-induced changes in reproductive physiology, and that the pars distalis of the pituitary gland contains an endogenous internal timer for the short photoperiod dependent development of reproductive photosensitivity. Here we report distinct seasonal waveforms of transcript expression in the MBH, and pituitary gland and discovered the patterns were not synchronized across tissues. Follicle-stimulating hormone-{beta} (FSH{beta}) expression increased during the simulated spring equinox, prior to photoinduced increases in prolactin, thyrotropin-stimulating hormone-{beta} and testicular growth. Diurnal analyses of transcript expression showed sustained elevated levels of FSH{beta} under conditions of the spring equinox, compared to autumnal equinox, short (<12L) and long (>12L) photoperiods. FSH{beta} expression increased in quail held in non-stimulatory short photoperiod, indicative of the initiation of an endogenously programmed interval timer. These data identify that FSH{beta} establishes a state of photosensitivity for the external coincidence timing of seasonal physiology. The independent regulation of FSH{beta} expression provides an alternative pathway through which other supplementary environmental cues, such as temperature, can fine tune seasonal reproductive maturation and involution.

zoology↗