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1. Species-Specific Expression of Growth-Regulatory Genes in 2 Anoles with Divergent Patterns of Sexual Size Dimorphism

   https://doi.org/10.1093/iob/obac025  

   Cox, Christian L.; Logan, Michael L.; Nicholson, Daniel J.; Chung, Albert K.; Rosso, Adam A.; McMillan, W. Owen; Cox, Robert M. (August 2022, Integrative Organismal Biology)

   Synopsis Sexual size dimorphism is widespread in nature and often develops through sexual divergence in growth trajectories. In vertebrates, the growth hormone/insulin-like growth factor (GH/IGF) network is an important regulator of growth, and components of this network are often regulated in sex-specific fashion during the development of sexual size dimorphism. However, expression of the GH/IGF network is not well characterized outside of mammalian model systems, and the extent to which species differences in sexual size dimorphism are related to differences in GH/IGF network expression is unclear. To begin bridging this gap, we compared GH/IGF network expression in liver and muscle from 2 lizard congeners, one with extreme male-biased sexual size dimorphism (brown anole, Anolis sagrei), and one that is sexually monomorphic in size (slender anole, A. apletophallus). Specifically, we tested whether GH/IGF network expression in adult slender anoles resembles the highly sex-biased expression observed in adult brown anoles or the relatively unbiased expression observed in juvenile brown anoles. We found that adults of the 2 species differed significantly in the strength of sex-biased expression for several key upstream genes in the GH/IGF network, including insulin-like growth factors 1 and 2. However, species differences in sex-biased expression were minor when comparing adult slender anoles to juvenile brown anoles. Moreover, the multivariate expression of the entire GH/IGF network (as represented by the first two principal components describing network expression) was sex-biased for the liver and muscle of adult brown anoles, but not for either tissue in juvenile brown anoles or adult slender anoles. Our work suggests that species differences in sex-biased expression of genes in the GH/IGF network (particularly in the liver) may contribute to the evolution of species differences in sexual size dimorphism. 

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2. Chigger mite ( Eutrombicula alfreddugesi ) ectoparasitism does not contribute to sex differences in growth rate in eastern fence lizards ( Sceloporus undulatus )

   https://doi.org/10.1002/ece3.10590  

   Conrad, Hailey; Pollock, Nicholas B.; John‐Alder, Henry (October 2023, Ecology and Evolution)

   Allen Moore, University of (Ed.)

   Abstract Parasitism is nearly ubiquitous in animals and is frequently associated with fitness costs in host organisms, including reduced growth, foraging, and reproduction. In many species, males tend to be more heavily parasitized than females and thus may bear greater costs of parasitism.Sceloporus undulatusis a female‐larger, sexually size dimorphic lizard species that is heavily parasitized by chigger mites (Eutrombicula alfreddugesi). In particular, the intensity of mite parasitism is higher in male than in female juveniles during the period of time when sex differences in growth rate lead to the development of sexual size dimorphism (SSD). Sex‐biased differences in fitness costs of parasitism have been documented in other species. We investigated whether there are growth costs of mite ectoparasitism, at a time coinciding with sex differences in growth rate and the onset of SSD. If there are sex‐biased growth costs of parasitism, then this could suggest a contribution to the development of SSD inS. undulatus. We measured growth and mite loads in two cohorts of unmanipulated, field‐active yearlings by conducting descriptive mark‐recapture studies during the activity seasons of 2016 and 2019. Yearling males had consistently higher mid‐summer mite loads and consistently lower growth rates than females. However, we found that growth rate and body condition were independent of mite load in both sexes. Furthermore, growth ratesandmite loads were higher in 2019 than in 2016. Our findings suggest that juveniles ofS. undulatusare highly tolerant of chigger mites and that any costs imposed by mites may be at the expense of functions other than growth. We conclude that sex‐biased mite ectoparasitism does not contribute to sex differences in growth rate and, therefore, does not contribute to the development of SSD. 

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3. Ectopic brain-derived insulin-like growth factor-1 partially rescues neuroanatomical defects associated with developmental hypothyroidism

   Alexandra, Grond; Saatman, Kathryn; Sharlin, David S. (November 2018, Abstracts - Society for Neuroscience)

   Insufficient thyroid hormone (TH) during development results in permanent neurological deficits. These deficits are the result of neuroanatomical defects that include smaller brain, fewer parvalbumin neurons, and hypomyelination. Interestingly, insufficient insulin-like growth factor 1 (Igf-1) during development results in similar neuroanatomical defects to those reported for developmental hypothyroidism. Thyroid hormone is known to indirectly influence serum Igf-1 levels through its regulation of pituitary growth hormone (GH) secretion which stimulates hepatic Igf-1 production. Our lab and others have observed decreases of local brain-derived Igf-1 in the developing hypothyroid mouse brain. This observation suggests that deficits associated with low TH during development may be the result of altered brain-derived Igf-1. Considering this, we sought to determine whether ectopically expressing Igf-1 in the developing brain could rescue neuroanatomical defects associated with TH. To accomplish this, the tet-off transgenic system was used where mice harboring tetracycline transactivator protein driven by the human GFAP promoter (tTA-GFAP) were crossed with mice containing the human Igf-1cDNA under the control the TET response element (Igf1-pTRE) transgene. Double transgenic (dTg) offspring carrying both the tTA-GFAP and Igf1-TRE genes overexpress Igf-1 specifically in brain astrocytes. The timed-pregnant mice were treated with thyroid gland inhibitors from embryonic day 14.5 (E14.5) until postnatal day 14 (P14) to induce a hypothyroid state in pups. At P14, pups were weighed and sacrificed, trunk blood was collected, and brains were dissected, weighed, and immediately frozen. Hippocampal structure, known be disrupted by developmental hypothyroidism, was assessed by fluorescent imaging using DAPI staining. Our initial results indicate that ectopic expression of Igf-1 in the brain (dTg mice) rescues hypothyroidism-induced reductions in brain weight without increasing body weight. In addition, the ectopic expression of Igf-1 restored hypothyroidism-induced perturbations in dentate gyrus size. Ongoing studies are using quantitative real-time PCR on micro-dissected cortical and hippocampal samples, to quantify myelin associated glycoprotein and parvalbumin mRNAs. Taken together, our findings support the idea that ectopic brain-derived Igf-1 rescues neuroanatomical defects caused by hypothyroidism and implicates TH in the regulation of brain Igf-1. 

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4. Vasoactive Intestinal Peptide Indirectly Elicits Pituitary LH Secretion Independent of GnRH in Female Zebrafish

   https://doi.org/10.1210/endocr/bqab264  

   Tanaka, Sakura; Zmora, Nilli; Levavi-Sivan, Berta; Zohar, Yonathan (January 2022, Endocrinology)

   Abstract Vasoactive intestinal peptide (Vip) regulates luteinizing hormone (LH) release through the direct regulation of gonadotropin-releasing hormone (GnRH) neurons at the level of the brain in female rodents. However, little is known regarding the roles of Vip in teleost reproduction. Although GnRH is critical for fertility through the regulation of LH secretion in vertebrates, the exact role of the hypophysiotropic GnRH (GnRH3) in zebrafish is unclear since GnRH3 null fish are reproductively fertile. This phenomenon raises the possibility of a redundant regulatory pathway(s) for LH secretion in zebrafish. Here, we demonstrate that VipA (homologues of mammalian Vip) both inhibits and induces LH secretion in zebrafish. Despite the observation that VipA axons may reach the pituitary proximal pars distalis including LH cells, pituitary incubation with VipA in vitro, and intraperitoneal injection of VipA, did not induce LH secretion and lhβ mRNA expression in sexually mature females, respectively. On the other hand, intracerebroventricular administration of VipA augmented plasma LH levels in both wild-type and gnrh3-/- females at 1 hour posttreatment, with no observed changes in pituitary GnRH2 and GnRH3 contents and gnrh3 mRNA levels in the brains. While VipA’s manner of inhibition of LH secretion has yet to be explored, the stimulation seems to occur via a different pathway than GnRH3, dopamine, and 17β-estradiol in regulating LH secretion. The results indicate that VipA induces LH release possibly by acting with or through a non-GnRH factor(s), providing proof for the existence of functional redundancy of LH release in sexually mature female zebrafish. 

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5. Caught in the middle: Variation in the physical and behavioral development of male olive baboons (Papio anubis)

   Hawks, Kale A; Most, Corinna A (March 2024, American journal of biological anthropology)

   Male baboons mature more slowly than females, reaching full adult maturity at around 10-12 years of age. After the onset of puberty at 5-7 years, the sub-adult period lasts 3-5 years while the male continues to grow, though there is considerable variation between individuals. Here, we present data on the behavioral changes that accompany the physical maturation of male olive baboons (Papio anubis) as they transition through each developmental stage. This research was conducted on a fully habituated wild troop at the Uaso Ngiro Baboon Project in Laikipia, Kenya. We use long-term grooming data (2018-2023) to show that males have significantly more grooming partners as they get older (n=48, p<.001). We then use behavioral data collected in June and July 2023 to compare the social behaviors of males from three developmental stages: juveniles (n=5), males who recently became sub-adults (n=4), and males who have been sub-adults for over a year (n=5). The differences between these three groups show the effect of puberty on behavior: juveniles were observed in social play significantly more often than sub-adults (p=.006), while males who recently underwent puberty tended to groom less often than either juveniles or older sub-adults (p=.091). Our focal data also revealed variation in the age at which males reached each developmental stage. Further research is needed to determine causes and consequences of the variation in age at puberty and the potential long-term consequences of this variation on the males’ social behavior. 

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