2 research outputs found
Serum testosterone, sex hormone-binding globulin and sex-specific risk of incident type 2 diabetes in a retrospective primary care cohort
__Objective:__ Previous studies suggest that androgens have a sexually dimorphic impact on metabolic dysfunction. However, the sex-specific link between circulating androgens and risk of type 2 diabetes mellitus (T2DM) has not been examined in a large scale, longitudinal cohort, a task we undertook in this study.
__Design:__ A retrospective cohort study in a UK primary care database.
__Patients:__ We included men and women with available serum testosterone and sex hormone-binding globulin (SHBG) results.
__Measurements:__ We categorized serum concentrations according to clinically relevant cut-off points and calculated crude and adjusted T2DM Incidence Rate Ratios (IRRs and aIRRs).
__Results:__ Serum testosterone concentrations were available in 70 541 men and 81 889 women; serum SHBG was available in 15 907 men and 42 034 women. In comparison to a reference cohort with serum testosterone ≥20 nmol/L, men with lower serum testosterone had a significantly increased risk of T2DM, with the highest risk in those with serum testosterone <7 nmol/L (aIRR 2.71, 95% CI 2.34-3.14, P < 0.001). In women, the risk of T2DM started to increase significantly when serum testosterone concentrations exceeded 1.5 nmol/L, with the highest risk in women with serum testosterone ≥3.5 nmol/L (aIRR 1.98, 95% CI 1.55-2.52, P < 0.001). These observations were verified in a continuous rather than categorized analysis. The risk of T2DM increased in men and women with serum SHBG <40 and <50 nmol/L, respectively.
__Conclusions/Interpretation:__ In this longitudinal study, we found sexually dimorphic associations between serum testosterone and risk of incident T2DM. Androgen deficiency and excess should be considered important risk factors for diabetes in men and women, respectively
Plant reproduction in the alpine landscape : reproductive ecology, genetic diversity and gene flow of the rare monocarpic "Campanula thyrsoides" in the Swiss Alps
Aims & Objectives
The work presented in this thesis forms part of a larger project “How patchy
habitat and isolation affect alpine plant life: genetic diversity, gene flow and mating
systems”, which includes the PhD studies of Patrick Kuss and the author under the
supervision of Professor Jürg Stöcklin.
This doctoral thesis investigates the consequences of the natural fragmentation
and patchiness of alpine landscapes on the life of alpine plant populations. The central
focus of the thesis is on the mating system, the role of inbreeding and/or outbreeding
depression, genetic diversity and geographic structure within and among populations
of the rare Alpine monocarpic perennial Campanula thyrsoides. The main objectives
and research questions addressed are:
• Is Campanula thyrsoides self-compatible (SI) and if not, does the SI system
break down with flower age? Do inbred C. thyrsoides offspring in the common
garden suffer from inbreeding depression?
• Do we find a distance related inbreeding depression (poorer reproducive
output) or outbreeding depression (increased reproductive output) in field
populations of C. thyrsoides following crosses of different crossing distances
(selfing, 1m, 10m, 100m and among distant populations)?
• How much genetic diversity exists within populations of C. thyrsoides and
how does it relate to population size and altitude? Has the natural habitat
fragmentation let to strong genetic differentiation and restricted gene flow
among populations of C. thyrsoides resulting in a pronounced geographic
structure?
Study species
In order to seek answers to our research questions, we choose to study a
yellow bellflower; Campanula thyrsoides. The choice was based on the information
that C. thyrsoides is a rare plant species, which is only found on calcarious soils
within the European Alps and adjacent mountain ranges (Aeschimann et al. 2005).
The plants selectiveness for carbonate bearing soils together with the fact that its
seeds are not adapted to long-distance dispersal (Tackenberg 2003) are the main
reasons for the isolation and small sizes of many of its populations. These population
characteristics, therefore, made C. thyrsoides a suitable study species. Another
important characteristic of C. thyrsoides, and one of the main reasons for its inclusion
in the study is because it is a monocarpic perennial which flowers once and
subsequently dies (Jäger 2000). Monocarpic plants species, which are more
commonly found in subtropical and tropical mountain systems (e.g. the giant rosettes
of Puya spp, Espeletia spp., Echium spp. etc., Smith & Young 1987; Young &
Augspurger 1991) are rare amidst the temperate alpine flora (for the Alps, see
Aeschimann et al. 2005). Monocarpy can promote genetic differentiation between
populations by reducing the effective population size due to a shorter generation time
and lower density of populations (Loveless & Hamrick 1984; Vitalis et al. 2004).
When studying the effects of population isolation and habitat fragmentation on
plant reproduction (e.g. mating system and inbreeding depression), it is, moreover,
ideal to study a Campanula species. Although most Campanula species are selfincompatible
and allogamous (Nyman 1993), both a break-down in the SI system with
flower age (Vogler et al. 1998) and an evolution towards complete self-compatibility
(Ægisdóttir & Thórhallsdóttir 2006) have been recorded.
Design
We studied the reproductive ecology and genetic diversity of Campanula
thyrsoides by firstly setting up pollination experiments in the common garden and in
the field and secondly by sampling leaf material in 32 field populations in
Switzerland. In the common garden study, we set up a pollination experiment in order
to study the breeding system of C. thyrsoides, including the consequences of selfing,
half-sibling crossings and outcrossing on reproductive output and seedling
performance. Moreover, field experiments in four populations were set up in the
Swiss Alps in order to study the effect of different crossing distances on reproduction
in C. thyrsoides and to see if evidence would be found of hidden inbreeding
depression or outbreeding depression following large-distance crossings compared to
within-population crossings. In addition, we studied the genetic diversity, gene flow
and geographical structure within and among 32 field populations of C. thyrsoides in
Switzerland, covering both large geographical and altitudinal ranges. The genetic
study was conducted using 5 co-dominant microsatellite markers. In addition, we
studied the genetic diversity in C. thyrsoides and two other alpine plants using random
amplified polymorphic DNA (RAPD) marker as well as studing the evolutionary
demography of C. thyrsoides