This study analyzes the effect of burning on the decay process, abundance of invertebrate fauna, and the diversity of invertebrate fauna in the pig liver samples; effect of the length of decay to the diversity of soil invertebrate fauna; and, the effect of the length of decay to the numbers of the soil invertebrate fauna. Two hundred grams (440 lbs) samples of pig (Sus scrofa L. ) liver were utilized in this experiment by exposing it to the grassland soil environment around Byrom Street Complex between 2 days and 4 weeks.
At day 3, 7, 10, 14, and 17 burnt and unburnt liver samples and five soil cores from underneath the liver samples were collected and placed at -20°C to prevent further degradation and multiplication of the invertebrate fauna present in the sample. Then the invertebrates present in the pig liver samples and soil cores were extracted, identified, and counted. The study results which were tested with a two sided t-test shows evidence that there is significant effect of burning in the abundance of invertebrate fauna in the corpse of vertebrate animal species.
Burning decreases the number of invertebrate fauna colonizing the dead body remains. The t-test analysis of the data gathered also proves the significance of the relationship between the rate of decay of dead body remains and the burning. The study concludes that the invertebrate fauna abundance does not increase in relation to the length of decay. The Effects of Burning on Diversity and Numbers of Invertebrate Fauna in Decaying Dead Bodies of Vertebrate Animals and Soil with Decaying Dead Matter INTRODUCTION
Decaying vertebrate remains are good food source for insects whilst these insects are also of significance in the decomposition of these remains. The scavenging invertebrate fauna of vertebrate body remains today is utilized as important tools in the identification of the time elapsed since the death of the body. Continuous research has been done on the matter thus the emergence of forensic entomology which is the employment of invertebrate fauna such as arthropods, earthworms, and slugs in determining the time elapse from the death of the vertebrate animals especially human beings(Gomes, 2006).
This field in forensic science known specifically as medicocriminal or medicolegal entomology which focus on the utilization of arthropod evidence for the criminal investigation of wrongful or unexplained deaths has gained significant importance in legal medicine(Tabor, 2004). Body temperature and conditions like rigor mortis or livor mortis are insignificant factors to consider during cases wherein the human carcass has been found days after his or her death. During these cases the insects that colonize the decaying dead human’s remains can provide information about the postmortem interval (PMI).
Evidence that can serve as tool for the measurement of the PMI can be provided by the age of the immature stages of insects existing in the human carcass(Gomes, 2006). Established data regarding the development of arthropods which are significant in forensic investigations on the dead body remains that are derived through various controlled studies are employed in the conduct of forensic entomology(Tabor, 2004). Various conditions though like the species of invertebrate animals to be considered and the climatic condition of the location of death affect the accuracy of the information provided by this forensic entomology(Gomes, 2006).
Thus, there is a necessity to conduct studies and establish arthropod colonization patterns in corpse of different locations of the globe. The progression of the global acceptance of forensic entomology in the investigation of criminal cases like murders catalyzed the various studies and researches conducted on this matter. The insects belonging to the family Calliphoridae which is commonly known as “blowflies” in particular are currently employed as biological clock for the determination of the time of death for more than two weeks.
Some of the other insects found to be of significant importance in forensic entomology are: Chrysomya spp. , Cochliomyia spp. , Lucilia spp. , Fannia spp. , Drosophila spp. , Musca spp. , Nasonia spp. , Tineola spp. , Geotrupes spp. , and Necrobia spp(Gomes, 2006). The earliest invertebrates which will colonize dead body remains of vertebrate animals including humans are the necrophilus fly species which are of the family Calliphoridae and Sarcophagidae.
When the maggots of these invertebrates arise, beetles which belong to the families Staphylidae, Silphidae, and Histeridae are the next ones to colonize the corpse because they fed on the maggots of the necrophilus flies. Beetles that are under the family Dermestidae are usually the late ones to colonize the dead body remains of vertebrates because they thrive on dry stages of decomposing corpse. In different locations around the globe there is variation in the patterns of invertebrate fauna colonization due to the variations in arthropod families thriving factors(Tabor, 2004).
The general objective of this study is to verify the utilization of invertebrate fauna as indicators of the time elapsed from the death of the vertebrate animal. The specific objectives of this study are to determine the following: the existence of the effect of burning on the decay process, abundance of invertebrate fauna, and the diversity of invertebrate fauna in the pig liver samples; effect of the length of decay to the diversity of soil invertebrate fauna; and, the effect of the length of decay to the numbers of the soil invertebrate fauna MATERIALS AND METHODS
Studies associated to forensic entomology use various types of carcasses like that of the dogs, pigs, and calves. In this study, samples of the pig (Sus scrofa) liver were utilized because whilst it is the widely utilized and acceptable animal model, humans have similar characteristics with this animal specie such as the type of digestive system and the omnivorous characteristic. Two hundred grams (440 lbs) samples of pig liver were utilized for the experiments. All the pig livers were placed on the same day on the surface of the grassland soil around Byrom Street Complex between 2 days and 4 weeks.
Wire coverings were utilized to prevent seagulls and other scavengers from consuming the pig liver samples placed in the grassland soil. All the samples have the same exposure to the weather and invertebrate infestation. The pig liver samples were of two types the burnt and unburned (control) samples. At day 3, 7, 10, 14, and 17 burnt and unburnt liver samples were collected and placed at -20°C to prevent further degradation and multiplication of the invertebrate fauna present in the samples. The unburnt and burnt liver samples utilized in the experiment were identical in number.
The liver samples which were used as the burnt variable were first covered with petrol before being burnt until crisp, dry, and black in the outer surface. In each same time intervals, five soil cores were collected from underneath the liver samples. The invertebrates which were present in these soil cores were extracted, identified, and counted. During the examination time, the pig liver samples from the temperature of -20°C were weighed and then the colour and the state of decay were noted. The invertebrates which were present in the in the pig liver samples were extracted, identified, and counted.
The larvae of flies were classified into first, second, or third instar. The taxonomic groupings like the phylum, orders, and genus of the invertebrates collected from the pig liver samples were included in the identification, classification, and recording of the invertebrate species present in the samples. The species considered in the identification and classification of the invertebrate fauna extracted from the pig liver samples were: species under suborder Nematocera, Stratiomyia species, Fannia spp. , Calliphora spp.
(blowflies), species of family Lumbricidae (Earthworms), species of class Gastropoda (Slugs), species of Subclass Acari (Mites), species of order Collembola, species of order Diplura, Superclass Myriapoda (Millipedes and Centipedes), and species of family Carabidae. All the observations were recorded and tabulated after the experimentation proper. STATISTICAL ANALYSIS There are a variety of data gathered in this study thus the t-test was employed not only once in the analysis of the diverse gathered data.
To determine the effect of burning on the abundance of invertebrate fauna in the decaying body remains a two sided t-test is done. The hypothesis (ho) is that the number of Calliphora spp. colonizing the decomposing vertebrate animal part is equal in the burnt and unburnt pig liver samples. The effect of burning on the rate of decomposition of body tissues was also analyzed through a two way t-test and the hypothesis (ho) is that the rate of decay process is equal in both the burnt and unburnt pig liver samples.
Abundance of invertebrate fauna in soil in relation to the length of pig liver sample decay is determined by a two sided t-test with the hypothesis (ho) that the invertebrate fauna abundance RESULTS The primary invertebrate fauna which was observed in this study is the blowflies or Calliphora species. There are other species that were extracted from the liver sample though but the numbers are lesser than ten for each species and compared to the number of the Calliphora species the collected other invertebrate species are insignificant in number.
The results of the two sided t-test done for the determination if burning has effects on the abundance of invertebrate species implies that indeed burning vertebrate animal carcass is associated with decreased number of Calliphora spp. compared to the invertebrate animal species collected in the raw pig liver samples. At ? =10%, the computed value for /ttab/ is 1. 622 which is greater than ttab =1. 303. Then hypothesis (ho) which is the number of Calliphora spp. colonizing the decomposing vertebrate animal part is equal in the burnt and unburnt pig liver samples was rejected.
Thus, the ha that is the number of Calliphora spp. collected from the raw pig liver samples are greater than the number of Calliphora spp. collected from the burnt pig liver sample is accepted. Therefore, there is significant evidence which supports that burning affects the abundance of invertebrate fauna colonizing vertebrate animal corpse by creating a condition that facilitates the decrease of the number of the invertebrate fauna being able to colonize the burnt vertebrate animal corpse.
The existence larvae in the control liver pig samples were observed only until day 7 and the stage of larvae development is in the 1st and 2nd instar in both the raw (unburnt) and burnt pig liver samples. On the 10th day, a reduction in the number of Calliphora spp. larvae is observed whilst there is the development of some of the larvae into the third instar stage hence the stages of larvae observed in this collection period were 1st, 2nd, and 3rd instars for the unburnt pig liver samples. In the burnt liver samples the larval stages were not identified.
On day 14, the numbers of Calliphora species extracted continued to decrease whilst the larval stages are 1st, 2nd, and 3rd instar for the unburnt pig liver samples. The Callipora spp. larvae collected from the burnt pig liver samples on day 14 are on the 3rd instar. On the 17th day a greater reduction in the number of Calliphora species present is observed but mainly the larval stage is the 3rd instar (Table 1). SAMPLES DAY 1 DAY 7 DAY 10 DAY 14 DAY 17 Raw liver sample 1 no larvae 1st & 2nd instar larvae 1st, 2nd and 3rd instar larvae 1st, 2nd and 3rd instar larvae no larvae
Raw liver sample 2 no larvae 1st & 2nd instar larvae 1st, 2nd and 3rd instar larvae 2nd and 3rd instar larvae 3rd instar larvae Burnt liver sample 1 no larvae 1st & 2nd instar larvae Larval stage not identified 3rd instar larvae 3rd instar larvae Burnt liver sample 2 no larvae 1st & 2nd instar larvae Larval stage not identified 3rd instar larvae 3rd instar larvae Table 1. The stages of larval development observed in the burnt and unburnt pig liver samples. The effect of burning on the rate of decomposition of body tissues (pig liver samples) were analyzed also using a two sided t-test.
Since the data on the burnt and unburnt pig liver samples have two replicates the average of this data was used in the analysis. A graph of this average shows the difference of the decomposition rate of body tissues in the raw state and the burnt state (Figure 1). There is an observable greater decrease in tissue mass of the raw pig liver samples onwhen compared to the tissue mass decay of the burnt pig liver samples. The two sided t-test analysis result reject the hypothesis (ho) is that the rate of decay process is equal in both the burnt and unburnt pig liver samples.
The computed value for /ttab/ at ? =10% is 1. 899. This is greater than ttab =1. 303 , thus the null hypothesis (ho) is rejected and the alternative hypothesis which is raw pig liver sample tissue decomposed (in kilograms) is greater than the tissue decomposed in the burnt pig liver samples. The rate of decomposition thus is faster in unburnt vertebrate body remains when compared to the burnt body remains. The number of invertebrate colonization in the soil in relation to the length of corpse decay in the different sample types is shown in figure 2.
In each sample type (control, raw, and burnt pig liver samples) there were 6 replicates thus the values of the replicates were averaged and then tabulated and converted into a graph. The graph shows that in both the raw (unburnt) and burnt pig liver samples the peak number of invertebrates collected is in day 7. There was greater number of invertebrates collected in the soil with burnt pig liver sample (average of 234 invertebrates) on the 7th day collection compared to the collected invertebrates in the soil with raw pig liver sample.
Abundance of invertebrate fauna in soil in relation to the length of pig liver sample decay is determined by a two sided t-test with the hypothesis (ho) that the invertebrate fauna abundance (number of invertebrates) increases in relation to the progression of the length of decay. The t- test result rejects the hypothesis (ho) that the invertebrate fauna abundance (number of invertebrates) increases in relation to the progression of the length of decay. The computed value for /ttab/ at ? =10% is 2. 278 which is greater than ttab =1. 303.
The invertebrate fauna does not decrease with the progression of the decay due to the life cycling of the invertebrates. DISCUSSION The predominant invertebrate species that first arrive in the dead body remains of vertebrates especially humans are the blowflies which belong to the family Calliphoridae and the members of these family are commonly known as Green bottle flies, House flies, and Blue Bottle flies. The stages of the life cycle of these flies are the egg, first instar larvae, second instar larvae, third instar larvae, prepupa, pupa, and adult(Steck-Flynn, 2003).
These species of invertebrate fauna are first colonizers of vertebrate dead animal remains hence there population are the predominant ones observed in this study. The pattern of colonization abundance in the soil is different in both the raw and burnt liver pig samples (Fig. 2). The colonization abundance in the soil with raw pig liver samples has a major and minor peak in the five collection days which is in day 7 and day 14 respectively. The invertebrate fauna collected on the soil with burnt pig sample on the other hand has the major peak also at day 7 but the other peak is not in the scope of the 5 collection days (day3, 7, 10, 14, &17).
The soil invertebrate colonization thus has a later cycle in the burnt pig liver sample when compared to the raw pig liver sample. The invertebrate fauna species that have majority of the population of the collected specimens were the blowflies (Calliphora spp. ). The other invertebrate species that has significant numbers in the collected population are: Mites, Collembola, Diplura, Carabid/ Staphylinid larvae, and Earthworms. The faster rate of decomposition of raw vertebrate dead body tissues when compared to the burnt vertebrate dead body tissues is attributed to the presence of more materials that the invertebrates can fed on.
The burnt tissues of invertebrate dead bodies have have lesser water content and the tissues are covered with carbon dioxide instead of oxygen. Palatability may be the reason behind the invertebrate animal’s preference for raw than burnt corpse. The lesser invertebrates that feed on the dead body remains the longer the decay of it hence the burnt dead body remains will take longer time to decompose(de Carvalho, 2001).
ACKNOWLEDGEMENT REFERENCES de Carvalho, L. (2001).Seasonality of insect succession and pig carcass decomposition in a natural forest area in southeastern Brazil Journal of Forensic Sciences, 46(3). Gomes, L. V. Z. , CL. (2006). Forensic Entomology and Main Challenges in Brazil. Neotropical Entomology, 35(1), 001-011. Steck-Flynn, K. (2003). The Role Of Entomology In Forensic Investigations. Crime and Clues Retrieved January 19, 2008, from http://www. crimeandclues. com/entomology_intro. htm Tabor, K. B. , C; & Fell, R. (2004). Analysis of the Successional Patterns of Insects on Carrion in Southwest Virginia. Journal of Medical Entomology, 41(4), 785? 795.
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