Breaking News
November 15, 2018 - Researchers develop tool that speeds up analysis and publication of biomedical data
November 15, 2018 - Scientists identify mechanism used by lung cancer cells to obtain glucose
November 15, 2018 - Abnormalities in development of the brain could be involved in onset of autism, finds new study
November 15, 2018 - Soy protein equally effective as animal protein in building muscle strength
November 15, 2018 - American Academy of Pediatrics, Nov. 2-6
November 15, 2018 - Dopamine drives early addiction to heroin
November 15, 2018 - Variance in gut microbiome in Himalayan populations linked to dietary lifestyle | News Center
November 15, 2018 - Reducing Cardiovascular Disease: The Amish Way
November 15, 2018 - King’s researchers launch charter to guide organizations to engage abuse survivors in research
November 15, 2018 - Enable Injections enters into development agreements with UCB and Apellis Pharmaceuticals
November 15, 2018 - TGen North collaborates with NARBHA Institute to advance human health
November 15, 2018 - Researchers discover molecular basis for therapeutic actions of an African folk medicine
November 15, 2018 - Human Cell Atlas study of early pregnancy shows how mother’s immune system is modified
November 15, 2018 - New guidelines for detecting and managing sarcopenia to be launched in the UK
November 15, 2018 - Researchers explore role of dietary composition on energy expenditure
November 15, 2018 - Elsevier launches Entellect™ Platform, unlocking value by creating AI-ready life sciences data
November 15, 2018 - Now that cannabis is legal in Canada, let’s use it to tackle the opioid crisis
November 15, 2018 - In the Spotlight: At the intersection of tech, health, and ethics
November 15, 2018 - Traditional Glaucoma Test Can Miss Severity of the Disease
November 15, 2018 - Researchers directly connect activities of genes with instinctive behavior in male cichlids
November 15, 2018 - Salk researchers report new methods to identify AD drug candidates with anti-aging properties
November 15, 2018 - St. Jude Hospital announces availability of largest collections of leukemia samples
November 15, 2018 - Attenua Announces First Patient Treated in Phase 2 Clinical Trial in Chronic Cough with Bradanicline
November 15, 2018 - Designing a novel cell-permeable peptide chimera to promote wound healing
November 15, 2018 - NEI investigators combine two imaging modalities to view the retina in unprecedented detail
November 15, 2018 - Determining how hearts develop to better understand congenital heart defects
November 15, 2018 - Maverick immune cells can act independently to identify and kill cancer cells, finds research
November 15, 2018 - Advanced AI and big data methods to tackle dementia
November 15, 2018 - Report reveals increase in pancreatic cancer death rates across Europe
November 15, 2018 - Luxia Scientific announces availability of its gut microbiome test in Luxembourg
November 15, 2018 - New diabetes drugs linked to increased risk of lower-limb amputation and ketoacidosis
November 15, 2018 - Lilly Submits New Drug Application to the FDA for Lasmiditan for Acute Treatment of Migraine
November 15, 2018 - Heart failure patients shouldn’t stop meds even if condition improves: study
November 15, 2018 - RetiPharma secures funding to develop new peptide drug for treating degenerative eye disorders
November 15, 2018 - Breakthrough research could lead to a new wave of cancer-fighting antibodies
November 15, 2018 - Mylan and Biocon launch new insulin glargine biosimilar in the UK
November 15, 2018 - For wildfire safety, only particular masks guard against toxic particulate matter
November 15, 2018 - New study of tribe shows influence of Western diet and lifestyle on blood pressure
November 15, 2018 - Scientists harness power of natural killer cells to treat children with neuroblastoma
November 15, 2018 - Investigating foodborne disease outbreak in Bosnia and Herzegovina based on simulation game
November 15, 2018 - Recommendations Issued for Management of Bradycardia
November 15, 2018 - Benefit unclear due to a lack of suitable studies
November 15, 2018 - TAMEST recognizes UT Southwestern’s Ralph DeBerardinis for changing our understanding of cancer
November 15, 2018 - Researchers discover key factors behind intestinal inflammation in CVID patients
November 15, 2018 - CityU develops first microarrayed 3D neuronal culture platform
November 15, 2018 - Expert suggests ways to control uncomfortable vaginal symptoms in diabetic women
November 15, 2018 - New edition of Red Journal focuses on roles of imaging in radiation oncology
November 15, 2018 - Doctors Aren’t Promoting Breastfeeding’s Cancer-Protection Benefit
November 15, 2018 - Collection of demonstration projects highlights value of patient engagement in research
November 15, 2018 - Technique to ‘listen’ to a patient’s brain during tumour surgery
November 15, 2018 - Seven-year-old returns to life as a “normal, healthy child” following bone marrow transplant
November 15, 2018 - AMSBIO expands range of high quality FFPE cancer cell line controls
November 15, 2018 - Marijuana use by kidney donors has no effect on transplant outcomes
November 15, 2018 - Exploring NMR Spectroscopy Applications through Interesting Infographics
November 15, 2018 - Chapman University wins additional $2.9 million NIH grant to study Alzheimer’s disease
November 15, 2018 - Microgel powder reduces infection and promotes healing
November 15, 2018 - Suicidal patients with prescribed access to psychotropic drugs should be closely monitored
November 15, 2018 - Nitric oxide-releasing technology shows potential to reduce healing time of diabetic foot ulcers
November 15, 2018 - Mass shootings may trigger unnecessary blood donations
November 15, 2018 - From heart disease to cancer: New study tracks shift of county death rates
November 15, 2018 - Preventing falls with new sensor technology
November 15, 2018 - Promising technology could improve detection, diagnosis of fatal ovarian cancer
November 15, 2018 - AAP updates concussion recommendations for children and teens
November 15, 2018 - Two genomic tests help identify most effective treatment for breast cancer patients
November 15, 2018 - Researchers evaluate efficacy of salivary biomarkers for early detection of oral cancer
November 15, 2018 - NIH awards $3.5 million to continue development of robotic system for treating brain tumors
November 15, 2018 - Researchers succeed in building protein nanotubes from tiny scaffolds
November 15, 2018 - Rectal bleeding
November 15, 2018 - Nasal delivery of weight-loss hormone eases breathing problems in sleeping mice
November 15, 2018 - $9.6 million grant to fund research on vascular risk factors for brain aging, dementia | News Center
November 15, 2018 - Gum disease linked with diabetes
November 15, 2018 - Study identifies unique functional brain networks associated with ASD behaviors in infancy
November 15, 2018 - EU and industry-funded project aims to personalize diabetes treatment
November 15, 2018 - NIH researchers shed light on causes of HBV-associated acute liver failure
November 14, 2018 - FDA Alert: Implanted Pumps: Safety Communication
November 14, 2018 - Weight loss & acute Porphyria
November 14, 2018 - Researchers identify three sub-types of depression
November 14, 2018 - The puzzle of a mutated gene lurking behind many Parkinson’s cases | News Center
November 14, 2018 - The mystery viruses far worse than flu
November 14, 2018 - Research highlights physical changes in the brain of self-injuring teen girls
The evolution of gigantism in tortoises continues to be enigmatic

The evolution of gigantism in tortoises continues to be enigmatic

image_pdfDownload PDFimage_print

Tortoises are a group of terrestrial turtles globally distributed in habitats ranging from deserts to forests and include species such as the Greek and the Galapagos tortoise. Some species evolved large body sizes with a shell length exceeding 1 metre whereas others are no larger than 6-8 centimetres. Despite a particular interest from naturalists ever since the times of Darwin, the evolution of gigantism in tortoises remains enigmatic.

The fact that all living giant tortoises are insular may suggest that their evolution followed the so-called island rule: a trend toward dwarfism of large animals and gigantism of small animals on islands. An example of insular dwarfism is the Florida key deer, a dwarf version of the mainland white-tailed deer; its small size may be an adaptation to the limited resources found on the islands. Insular gigantism is best exemplified by the famous dodo, an extinct flightless pigeon from Mauritius, probably evolving large body size due to release from predatory pressure. Previous studies on extant tortoises were partly inconclusive: giant size has been linked to the absence of predatory mammals in islands but it has been also proposed that tortoises were already giants when they reached the remote archipelagos. Since very few giant tortoise species survive to the present, these hypotheses are impossible to test without analysing extinct species through the help of the fossil record.

In a recent study in the journal “Cladistics“, Dr Evangelos Vlachos from the Paleontological Museum of Trelew, Argentina, and Dr Márton Rabi from the Martin Luther University Halle-Wittenberg (MLU), funded by the German VolkswagenStiftung, assembled the most comprehensive family tree of extinct and extant tortoises so far. The researchers analysed genetic data from living species together with osteological data from fossil and living tortoises.

This is the first study of such global scale to allow for investigating body size evolution in tortoises. The fossils reveal a very different picture of the past compared to the present. Giant size evolved on multiple occasions independently in mainland Asia, Africa, Europe, North and South America at different times of Earth history. However, all of these species went extinct at latest during the Pleistocene ice age.

“The fossils highlight a great number of extinct mainland giant species and suggest that the evolution of giant size was not linked to islands,” says Dr Evangelos Vlachos.

Instead, living insular giant tortoises, such as the ones from Galapagos and Seychelles, more likely represent survivors of unrelated giant species that once inhabited South America, East Africa, and/or Madagascar.

“Giant tortoises may have been better island colonizers because they can tolerate water and food shortage during an oceanic dispersal for a longer period than smaller species. Giant tortoises have been reported to survive 740 km of floating in the ocean,” says Dr Márton Rabi.

What led to the extinction of these mainland giants remains enigmatic. For the ice age species, it may have been a combination of predatory (including human) pressure and climate change. It is likewise unclear, if not the island rule, then what is driving tortoises to repeatedly evolve into giant forms?

“We expect that warmer climate and predator pressure plays a role in the evolution of giant size but the picture is complex and our sampling of the fossil record is still limited.” – Vlachos adds.

An unexpected outcome of the study was that the Mediterranean tortoises (familiar due to their popularity as pets) actually represent a dwarf lineage as their ancestors turned out to be considerably larger.

“Tortoises have been around for more than 55 million years and we are now able to better understand the evolution of this successful group. Today, however, out of the approximately 43 living species 17 are considered endangered and many more are vulnerable largely due to human-induced habitat loss; this is a disappointing fact.” – Rabi points out.

Source:

https://www.uni-halle.de/

Tagged with:

About author

Related Articles