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Introduction: Unpaid caregiving, care provided by family/friends, is a public health issue of increasing importance. COVID-19 worsened the mental health conditions of unpaid caregivers, increasing substance/drug use and early development of chronic disease. The impact of the intersections of race and ethnicity, sex, age and gender along with unpaid care work and caregivers' health and well-being is unknown. The aim of this study is to describe the inequities of caregiver well-being across the intersections of race and ethnicity, sex, age and gender using a cross-sectional survey design., Methods and Analysis: We are collaborating with unpaid caregivers and community organisations to recruit a non-probability sample of unpaid caregivers over 18 years of age (n=525). Recruitment will focus on a target sample of 305 South Asian, Chinese and Black people living in Canada, who represent 60% of the Canadian racial and ethnic populations. The following surveys will be combined into one survey: Participant Demographic Form, Caregiver Well-Being Index, interRAI Self-report of Carer Needs and the GENESIS (GENdEr and Sex DetermInantS of Cardiovascular Disease: From Bench to Beyond-Premature Acute Coronary Syndrome) PRAXY Questionnaire. Sample characteristics will be summarised using descriptive statistics. The scores from the Caregiver Well-Being Index will be dichotomised into fair/poor and good/excellent. A two-stage analytical strategy will be undertaken using logistic regression to model fair/poor well-being and good/excellent well-being according to the following axes of difference set a priori: sex, race and ethnicity, gender identity, age, gender relations, gender roles and institutionalised gender. The first stage of analysis will model the main effects of each factor and in the second stage of analysis, interaction terms will be added to each model., Ethics and Dissemination: The University of Toronto's Health Sciences Research Ethics Board granted approval on 9 August 2022 (protocol number: 42609). Knowledge will be disseminated in pamphlets/infographics/email listservs/newsletters and journal articles, conference presentation and public forums, social media and through the study website., Trial Registration Number: This is registered in the Open Sciences Framework with a Registration DOI as follows: https://doi.org/10.17605/OSF.IO/PB9TD., Competing Interests: Competing interests: None declared., (© Author(s) (or their employer(s)) 2023. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.)

Although the endocrinological mechanism controlling regression of the internal, larval gills of anurans (frogs and toads) is well understood, the mechanism regulating loss of the external, embryonic gills is not known. Based on the homology of the mammalian ductus arteriosus with a portion of the amphibian branchial arches, and the regulation of blood flow in the mammalian ductus by prostaglandins of the E family (PGEs), we hypothesized that anuran external gill loss is also regulated by PGEs. To test this hypothesis, we topically applied both PGE2 and a synthetic analogue of PGE1, misoprostol, to embryos and young hatchlings of the red-eyed treefrog, Agalychnis callidryas. Both agents accelerated external gill regression. Furthermore, misoprostol overrode the inhibitory effect of hypoxia on gill regression in hatchlings and induced rapid loss of external gills in embryos, which normally maintain the gills until hatching. These observations support the hypothesis that PGEs regulate anuran external gill loss. The specific site of action for prostaglandins within the gills is not known; however, PGEs are secreted in the oral mucus of tadpoles, and this could be a natural topical source for these agents. PGEs offer a tool for manipulation of external gills and should facilitate tests of the physiological importance of these structures.

I examined the effects of development, hatching, and oxygen availability on external gill loss in red-eyed tree frogs, Agalychnis callidryas. Under natural conditions, the arboreal embryos maintained large external gills until hatching, which occurred from 5-8 d after oviposition. At hatching, when tadpoles entered the water, external gills began to regress. In older hatchlings this process was extremely rapid. Gill circulation was lost on average within 16 min and sometimes within 5 min. Gills often regressed completely in under 2 h. Younger hatchlings reduced gill circulation, shortened and adducted their gills, then resumed normal circulation for some time after hatching; half had completely lost external gills within 24 h. Experimentally increasing the area of egg surface exposed to the air induced loss of external gills in unhatched embryos. Older hatchlings in hypoxic water without access to air maintained their external gills. This suggests that loss of external gills is a response to increased oxygen availability, rather than a response to hatching per se. Extended maintenance of external gills by large, late-hatching embryos may facilitate continued rapid development in closely packed eggs.