Bat skulls in 3D – interview with Giada Giacomini

Giada Giacomini, the talented young Italian bat researcher came from the Liverpool John Moores University to the Mammal Collection of our institute. She has just started her PhD studies on the morphology of bat skulls and the connection between morphological variations according to echolocation parameters and geographical patterns and  her project is already awarded with the Synthesys fund to visit five European collections. The Hungarian Natural History Museum seemed to be an ideal place to start her studies, since the Mammal Collection holds a lot of bat species from Europe and various parts of the world.

In addition to the details of her work including 3D modeling, Giada has also shared some really  interesting facts about bats in this interview. 

What is the purpose of your visit?

Working in the Mammal Collection of the Hungarian Natural History Museum is inevitable because of two reasons. The first one is the extensive geographical distribution of the samples, the second is the amount of metadata including the gender and the age of the animals, which is fundamental for my research. This collection is the biggest that I have ever seen, holding  a lot of specimens in very good condition. The main objective of my Synthesys project is to collect pictures of bat skulls and build a 3D model out of them. Successively, employing the geometric morphometric approach I will place landmarks (=homologous anatomical points) on the model surface to study the size and shape variation of the samples. 

Could you show us the process of 3D modeling?

The first step is to capture high quality pictures of the skull following a precise protocol for the photo acquisition. I put the skull on a turning table in front of the camera and shoot long exposition photos to get a wide portion of the picture in focus. Because of the slow shutter speed ,I use remote control which helps me avoiding movement and the so called noise during the long exposition. For each picture, I turn the table 10° more or less until I rotate samples around 360°. Successively, I process the pictures with a specific  software for the 3D modeling. This software is very memory demanding, so unfortunately, I cannot show you the whole process now. I have to wait for the 3D reconstruction until I go back to Liverpool where I can work on an appropriate computer. After around 1 hour and 30 min of processing the model is ready for all the future analysis. The teeth are crucial to reproduce properly because they are quite shiny and can be rather tiny, so sometimes photos lack precious details of dental morphology.



Rhinolophus ferrumequinum (Giada Giacomini, Liverpool John Moores University)

Do you exclusively rely on morpholocial studies or also do molecural and phylogeographical examinations?

I have not had the chance yet to include genetic analysis since it would be „biting off more than you can chew” for a single project. But I am including the updated phylogeny in my study trying to undestrand if the morphological differences between the species are due to a shared evolutionary history or to a functional adaptation. 

Does your project or your work in general have any broader ecological aspects?

As with all morhological studies this project improves our understanding of the relationship between ecology and morphological adaptation. Once a relationship between a morphological trait and a funtctional characteristic is determinated, it will be possible to predict some ecological related aspects of those species which are not as well known. A better understanding of bat ecological needs will allow a better protection and conservation of their populations.

What is the basic ecological role of bats?

The first thing that came into my mind is that bats have a significant role in controlling pest as they eat insects that might be harmful for agriculture. Believe it or not, there are also many bat species that pollinate flowers because they feed on nectar such as butterflies or bees. The fruit –eating bats also have a fundamental function in plant seed dispersal.

So it also means that different species have different feeding habits. Could you tell us more about it?

That is correct. In Europe we mainly have insect-eating bats, but in the tropics the feeding habits spread in all the possible categories: carnivorous, frugivorous, nectarivorous, insectivorous, hematophagous and piscivorous. Yes, you understood well. There are bats able to fish. Thanks to echolocation they can assess the closeness of the fish to the water surface and catch them with their feet.

Plecotus austriacus (Gray Big-eared Bat)

What is it about the so called vampire bats?  Can they be harmful for humans?

In reality they feed almost exclusively on livestock and birds. It can also happen that they feed on humans,   but quite rarely. Consider that there are more than one thousand one hundred bat species exist in the world and just three of them are hematophagous.  All three species live in the tropics and only one spread through the temperate area, in some regions of Chile and Argentina.

Is there any connection between the different feeding habits and major morphological differences?

Surely there are. The skull morphological variation due to the feeding behavior is displayed in each level: from the whole shape of the skull to the tiny difference in the teeth. For example, bats feeding on plant nectar tend to have very long nostrils to be able to reach the bottom part of the flower, while frugivorous and insectivorous bats have a shorter and compact skull. There is also a strong correlation between tooth morphology and diet preference, for example insect-eating bats have a quite specialized molar structure due to the hardness of their prey. 

Figure 1- Readapted from Freeman 2000 (Freeman P. W., 2000. Macroevolution in Microchiroptera: recoupling morphology and ecology with phylogeny. Mammology papers: University of Nebraska State Museum. Paper 8.)

Apart from this project in which examining specimens held in collections is the major part of your work, you may also often go to field work, as well. What kind of habitats do you visit and how can you capture bats when you are there?                       

There are different techniques to capture them carefully and efficiently. If you are in a cave, and if they are close enough, you can pick them from the wall. It is like shopping in the supermarket when you put products in your cart. If the ceiling of the cave is high, you need a kind of butterfly net with long poles to capture them. Outside you can use a special armless net called a mist net fixed up to 5-6 meters high and placed on a bat commuting route. Bats fly into it and get trapped because of the looseness of the net.  Another tool to catch bats is the harp trap which is usually located in small entrances of forest tunnel or cave branch. In this case bat collides with the plastic filaments and fall inside a bag. 

Do you take the bats with yourself for further research or you take  samples in the field ?

It depends on the research you would like to do. In the majority of the cases you do not bring the bat home but you just collect data or sample out of it. For example, if you study the habitat the bats use, you just need to check the species and the gender and then you let them go. For genetic analysis, you take a small piece of the skin of the wing during the field activity and then release the bat immediately in the site.  Or if you are building a sound library, you will then need to identify the species  and the gender and record their ultrasonic sounds. Bat parasite collection might be another reason why you trap bats. It is a very interesting field and is possible to study the  coevolution between bats and their parasites. On the other hand, sometimes you can find new parasite species.

Is this always necessary to capture the animal to identify them?

 Based on a significant database of ultrasound you can identify bats without capturing them.  This method is deeply used in Europe where researchers have been working on bat call description and identification for decades.Yet  it is not always easy to discriminate between species from their echolocation sound.

What is the role of echolocation in the life of bats?

Bats are adapted to nocturnal and crepuscular life.  They are able to build an acoustic image of the environment which allows them to discern the environment from the prey. When bats are approaching a prey, the echolocation signal changes very fast and the frequency band increase dramatically to achieve a higher level of details. Bat echolocation is not important to bats only for commuting and for feeding, it is essential even from a social prospective. There are bats that sing  indeed for example, the noctule bat and Nathusius’ pipistrelle. The males are famous for their complex calls which they use to attract the female during the reproductive season.  Furthermore, echolocation signals can be used as distress codes to communicate the presence of a threat. 

Rhinolophus ferrumequinum

Horseshoe bats  (Rhinolophidae family)are different from the other European bats because they evolved a unique echolocation method. As other bats they use the larynx to produce sound but they emit ultrasound from their nose instead of using their mouth. On their nose there is a chamber where the sound passes through and goes outside in a very directional beam. Researchers found a relation between the echolocation frequency and the size of this chamber. The bigger the chamber, the lower the frequency of the sound that the bat emits.

Bat skulls in vial

So do you have an hypothesys on the connection between geographical and the morphological variations and how it affects the echolocation?

There are just a few clear informative facts about the drivers of bat geographical variation. There is an evidence that bat morphology changes according to the Bergmann’s rule: the size of the body increases with the increasing of the latitude. But on the other hand, doubts have been raised on the validity of this theory in all bats species.
Furthermore, the echolocation parameters can slightly variate within the species according to a geographical pattern. Those changes might be due to both “cultural drift” and morphological variation.  For the moment I have more guesses than proper hypothesis, but I hope to be able to answer your question in a more appropriate way at the end of my research.

Rhinolophus ferrumequinum (Greater Horseshoe Bat)

Where do you continue your Synthesys research?

I am at the beginnig of my project, so the Hungarian Natural History Museum  is my first stop within the Synthesys program.  I will also visit other significant institutions, such as the natural history museums in Vienna, Paris, Brussell and Copenhagen.

What is your expectation from the different collections? Do they have pecularities?

Each collection that I will visit cover a specific region of Europe with its specimens. The Hungarian Natural History Museum bat collection presents more than 2000 bat skulls mainly form eastern Europe. The Natural History Museum Vienna bat collection houses more than 900 specimens suitable for this study with necessary metadata available. The collection is mainly focused on Austria, Bosnia, Greece and Cyprus, Croatia, Hungary and some Polish, Romanian, Slovakian, Czech and Serbian records.  The Hungarian and Austrian collection together are of paramount importance to build an exhaustive database able to represent the eastern European bat variability. Paris  and Brussell museums, on the other hand, will give me the possibility to collect data on western Europe, while the Danish collection houses specimens mainly from northernEurope. The access to all those outstanding collection will also allow me to include rare specimens as Myotis punicus or Nyctalus lasiopterus.

Nyctalus noctula (Noctule)

Written by: Krisztián Kucska, Bernadett Döme

Photos by: Szabolcs Simó (skull photos by Giada Giacomini)